Hi! complete novice here. I have a shower/tub that has a bumpy floor. I've tried everything I can think of to get the floor back to white, but I can't do it. It looks dirty. I got to looking at it the other day and it seems like where it looks dirty, it's actually where the white has came off (I'm guessing while I was going scrub-crazy). Is there anything I can do to fix this?