How to repair a floating/popped up inground fiberglass pool?

I recently installed my 14 X 30 inground fiberglass pool. Last night, there was a pretty bad storm and I'm guessing that a lot of rain fell. When I looked at the pool today, It popped up out of the ground about four inches. before I installed the pool, I inserted a pipe that leads to beneath the pool so that I can drain out any water just in case it went under. I drained out all of the water and filled the pool completely and nothing happened. Please help me I really need to know how to fix it. Also there is no decking around the pool yet, just dirt.