Thanks for playing! I spent too much time working on the player controller scripts and didn't start working on Level 3 until about 3 hours before the deadline :O. I wanted to create jump through platforms for this level which would have made it a lot less frustrating.
You actually can pick up the trampoline shroom after you place it. Grab it like you would the dead shroom and then throw it to a new spot. You can find the soul gems by creatively placing/picking up the trampoline shrooms, especially in level 2.