How do I patch a gap between my bathtub and wall?
Depending how badly it was cut, sometimes the only complete solution is a new tub. At minimum, you need to re-cover the wall so that water on the wall runs into the tub - this may require new tiling or a tub surround. Any time a tub is replaced, the walls around the tub need to be done over, or leaks are almost guaranteed. The image is from a ceramic tile site, but the general idea is the same regardless of material - the wall must overlap the tub.