Are the blocks all the same pattern? If they are don't worry about them being smaller. Being a consistant size is more important. If getting them all the same size requires a little trimming, without seeing the blocks, I think it would be alright. I only worry about different size blocks if I'm doing an exchange or a sampler where all the blocks are different. Since all your blocks are a little smaller than you wanted, the sashing should work fine just trim a little if needed.