(Shout out to TheFox7771) Once we go out of bounds in Act 2-1 we continue on. Don't go back to get the Red Gems. You need to get the second strawberry in Act 2-1 to perform the glitch. The strawberry is located just before the the first mini boss. The area with the 4 breakable walls. The strawberry will be behind the 1st breakable wall on the left.

You also need to get the strawberry in Act 2-3 located to the right of the ladder in the alley.

[Update: You can still perform the Red Gem glitch, but make sure when you get to Act 2-2 (Cannibal Carnival) you quit, and reload the save. The strawberry should reload back into your inventory.]