I had a chance to think about this again and realized there was a better way to do this and you only need one sheet of 12 x 12 card stock for the card.
Finished card size 6″ x 6”
Score your card stock at 6″ and 6″ as shown in the image below. Also score the lower right square from inner corner to outer corner to for the pocket.
Cut away the lower left square
Fold on the diaganol score line and then on the horizontal score line to form the pocket. Close the card to insure everything lines up, if not then remove a bit from the edge with your paper trimmer. When everything is lined up, use 1/4″ tacky Tape to secure the first and second folds of the pocket card. Make sure the tape is right against the outer edge of the card.
The inner card of this example has a finished measurement of 5 1/4″ x 5 3/4″
Decorate the front of the card as you wish.
Here’s another look at the inside of the card.
This in not an original idea, just my interpretation of an image found online.