I also had a problem with the "add-a circuit" product when I installed my guages. I ended up modifying the body of the adaptor that pushes into my fuse panel.
Later I purchased another one and was amazed at how well it worked. Great product... if you get one that came from the right mold.
Check the sides of it, it should be molded just like the fuses are. If not take it back and exchange it for one that is.
And yes they do require quite a push to insert, but simply will NOT go in if built wrong.
Dsl_Duo