When my plane is on the ground and I use the slew option my plane would just launch foward (like stepping on the gas in a car with the parking brake on....release the break and the car launches foward) after I hit the "Y" key to get out of the slew mode. How do I stop this from happening?

This will happen if the sim detects that you're not on the ground. It attempts to place you in flight at a reasonable airspeed for the aircraft. To make sure you're on the ground, press the F1 key before coming out of slew.