Hi. the die that you are using (the largest Spellbinders Classic Oval die) is too wide for the 5 1/2" square card in the SCS tutorial. You need to increase the card to a 6" square card to accomodate the wider width. My original tutorial on my blog is for the 6" square card and you can find it here:
From My Craft Room: Peek-A-Boo Card Tutorial (6" or 15cm square)
Also, the original way of doing the back of of the card will hide the mechanism.
PS. I altered things for the SCS tutorial because 5 1/2" cards seem to be a favorite card size among SCS crafters (while 6" is my fave card size...hee hee) and the way of doing the back seem to be easier.
Hope this helps.