Gap between tub surround and tub?

The previous homeowners seemed to DIY with the tub surround using a white caulk strip instead of caulk. The strip did not last very long and if you lean slightly on the tub surround it gives or (bends) into the wall. I am not sure if the surround needs to be re-fitted to the bathtub or if caulk will stabilize the surround. Any suggestions would be greatly appreciated!