Vette Body Problems

K. I jus built a Sb hybrid motor, and put it in my vette. I ran it for a little while with-out the body, just to see how well it works, and then i wen to put the body on, and it doesn't fit anymore! I left the batteries in theri original place, the bottom plate is in the right spot, and the motor is all the way down. Does anyone know what my problem might be? I can get it on if I push down on the back bumper pretty hard, but it just slipped on before.......