Installing a new alcove tub in my fixer upper. Instructions say, build a 60 in opening. Drawings show a 60 in opening. I built a 60 inch opening. Tub is exactly 60 inches. Which means it wont fit. Looks like I can move the wall at the foot of the tub with a little careful work with a demolition saw. I had assumed that if the instructions call for 60 inches, then the tub would be 59.5, or something less than 60. Where did I go wrong?