I started over with a new code but the same idea. My game works by manually copy and paste the code instead of having a loop inside a loop.
LET tileNum = 0
LET ty = 40
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT
LET ty = ty + 10
LET tx = 40
FOR a = 1 to 30
LET tileNum = tileNum + 1
LET tileNum = tileNum + screenPos
LET tx = tx + 10
SETPENCOLOR colA(tileNum), colB(tileNum), colC(tileNum)
DRAWSTRING tile$(tileNum), tx, ty, "Courier", 15
NEXT