Looks good. one way to offset the 'tiling' aspect is to make the BMP scale larger (if it is scaled at 10, make it 20).

The other issue to move your GRID sheet up the list so it is placed Under the walls (the SHEET list is drawn top to bottom so whatever is on the TOP of the list is drawn first, then so on down the list till the Bottom which is drawn last).

As to your other question, the simple answer is:

"Before drawing anything Double check your SHEET"