The upper section of my bathroom wall is curving outwards (convex). The curved section begins at the ceiling and runs 36" down by 54" across and curves across the 54" length. The wall is comprised of drywall and you can see the curve running against the ceiling as well (again, it curves gently across 54").

I noticed this when I was trying to install a new towel rack (the two base ends would not stay flush against the wall). Currently, I have a towel rack installed on the lower half of the wall, which is not curved, but would love to get this fixed so that I can finally get the new one installed higher up.

Is there any way I can make the wall flat enough to install the new towel rack? Thank you!