So what I did was fitted up there like you did and determined I needed about 3/4 of an inch out of each side to fit nice and snug to within an eighth to a quarter of an inch... after that, I measured the whole thing measured center and then pulled back to what I felt was 1/4 of the way and try to do that evenly on both sides top and bottom to the best I could... then I put a piece of 3/4 inch wide blue tape down for what i wanted cut it out. Then I put a piece of tape on either side of that and pulled that original tape out of the center and made my cut there...