How did you do that?

Start a new game and name the profile TRGSVPPW. You should be notified that this activates a cheat code, and asked to confirm the activation. Select 'Yes.' You will be returned to the name entry screen, where you may name the profile as you wish. When you start the game, Shovel Knight should be 4 times wider and taller than normal. For another fun game variant, try entering the code as WSWWAEAW.

...However, I recommend first playing through the game at least once before using codes. Also, any playthrough with a code is locked out of Feats.