Are they coming out as rectangles or as too-small squares? Either way, you seem to have a couple options:
1) Make it creative! Add a 1/2" sashing between a pair of squares to get your quilt back on track. Or add 1/4" to the edge of your block. Or go really crazy & foundation piece wonky seams until your blocks are the intended size.
2) Work out the math. Adjust your blocks to accommodate the smaller sized squares (if they're rectangles, square up first, then work with them). You may end up needing an extra row or column, or an extra border, but if you really love the fabrics, it's worth it to figure out how to work them in there.
