Plumbing and Piping - shower walls

I have a unique problem that I have never had before,I have the tub and shower walls,not a one piece tub and shower walls,somehow ,someway I have developed a couple of cracks in the center piece of the shower wall,I have put clear silicone sealant on it to keep water out of behind them ,but I think I'm a little late,what I would like to know is;does anyone know of anything i can use to patch the area that is cracked for the matter of evening it out i am going to get a new tub and shower surround but wasn't wanting to do it this soon,as i previously stated i have got it sealed to keep water out and now it's mainly for cosmetic purposes because it looks horrible,i also realize that whatever i will need has to be waterproof or something that i can waterproof,any advice would be greatly appreciated,
Thanks Much!!
ms-p