Usually, you can fudge the location of the toilet maybe 1/4" or so on the flange. Moving it an inch probably won't allow you to get a proper wax seal since the horn on the toilet would be so far off from the sealing surface of the flange.
Measure from the finished wall to the holes for the toilet bolts - that's your rough-in location. Nominally, the toilet was probably a 12" version (and there's normally at least a little gap behind). You may end up needing to either look for a new toilet that will fit, move the toilet flange, or take off the tile behind the back of the toilet.