I have a shower stall with plastic walls that don't meet the floor. The walls seem straight, but it must have been cut crooked. I have up to a 1" gap between the wall and the shower floor. I have tried to caulk a couple of times, but it doesn't stick to the stall walls (I have tried to sand it but it still won't stick. Any suggestions? I am not worried about aesthetics, just functionality. Thank you.