Designing Kitchens and Bathrooms - Bathtub Surround

I have gutted my bathroom down to the wall studs. I have put in a
new Lasko soaking tub and have gotten it to be as close to level as
I think I can get it. However, when I put the back wall of the surround
(screw to stud surround) the gap between the tub and the bottom of the
surround is fairly even from the right going to the left until the surround
goes around the left corner of the tub (towards the faucet) then it comes
out about another 1/8 of an inch. Now I know this doesn't sound like much
but when the front panel goes on and has to line up with the back one the gap is pretty noticable and I don't think caulk will hold in it. I had started
to sand down the corners of the surround that sit in the corners of the tub
and have had no luck on getting the gap to shrink. Any ideas on why that
one section would have a greater gap coming around the corner like that?
I was thinking the wall studs may be preventing it from coming down flush.
Help..

Thanks in advance.
Melisa

Have you put a straight edge on the studs to see if they're even?

Thanks for such a quick response.

They come in slightly (very) but I don't see that it's enough to make a difference.
Would that prevent that little edge from coming down all the way?

Between that and if the tub is a little off level, yes.