Ok, you have 4, 8, 12, 8 and 4 right?
One of sets of 4 can go in the center
One set of 8 surrounds that creating a diamond type design
The set of 12 surrounds the diamond making a larger diamond
The second set of 8 begins the corner triangles squaring it up
The final set of 4 finishes the corners creating your completed square
If you consider your sets of 4 as A & E, your sets of 8 as B & D, and your set of 12 as C....
E D C C D E
D C B B C D
C B A A B C
C B A A B C
D C B B C D
E D C C D E
Now you just have to figure out which ones work best as which letter and how to twist and turn them to your satisfaction!
I think it will be really cute when you get done.
Let us know how it works out!