Your oil pan is probably glued on with the gasket. Drive a putty knife between the gasket and the block, the start working around until it comes loose. Be careful not to bend the oil pan flange. It can be straightened, but it is better if you don't have to. Also, when you do get it apart, it is common practice to tap the holes in the front main bearing hub and put the bolts in the timing cover in from the front so you don't have to drop the pan the next time.
