I just installed a sterling tub in my bathroom and the old shower valve does not stick enough for me to get the trim back on.

First, a little background. We bought our house two years ago. The previous owners had done some shoddy plumbing work in the bathroom. The old shower valve was leaking, and knowing that I would eventually want to replace the entire tub/surround, I installed a Delta shower control. There is no access panel because the vanity is built into an alcove next to the shower, so I had to cut open the wall to access the valve and install the new one.

Now, I have installed the tub and surround only to realize that the new surround wall is much thicker(in terms of distance from the studs), and of course I did not check to see if it would fit beforehand. The surround wall has been clipped in and I can't see how to get it off to fix this. I really don't want to break through the wall on the other side again, and I am not sure that it would help anyway.

Is there anything that I can do? Thanks in advance.