Hmm, so you want to just use the 3 size squares in the same quilt without cutting them? Those sizes don't play well together, so you might want to add some sashing to take the smaller squares up to the 8" size.
If you want to make 3 quilts, using only one size square in each, check out the moda bake shop:
http://www.modabakeshop.com/p/recipes.html
Look for patterns using charm squares. Charms are 5", so you will have to adapt the pattern for the 3" and 8" versions.