I have a problem I think anyway I have a 27ft by 52in round pool when we first started to fill the pool everything was level we started filling the pool and after about 3ft of water I checked the depth and it was almost 3in lower on one end of the pool my father-in-law said it would be OK as long as the top stayed level it don't sound right to me but I need help please...

If it ins't level with 3 ft of water in it, it won't be level with 4 ft. If the difference is just 3 inches, it's probably okay. Call a local pool store and ask them. This is why it's important to set the pool on a level concrete pad (or level ground).