Another Duck Dive Question

Having a hard time duck diving my new board. I can get the board under water but when I go to press down on the back of the board the whole board tries to come up but not darting up like I know it should. The board is just rising back to the top kinda of diagonally, if you know what I am saying... Is this board just too big to dive or is my technique off. Its like I cannot press hard enough to get my nose to shoot up first. Any ideas or help?