When you're doing the Alter Ego minigame don't pick up any of the yellow or red power ups. You have to pick up 5 of the yellow ones to level up so it's okay to collect a few on accident, but the red ones will level you up as soon as you pick it up.
If you're not sure which minigame this is, it's the side scrolling shooter one, where you're flying around as a tiny bentley.