Welcome to the board! I also am from Washington, Olympia on the West side of the state. If you have already sewn your 9 patch blocks together, measure each block to see how much you need to square up prior to cutting. If you only need to trim a little bit, then go ahead and square. If you have more than an inch of cutting on any block, you may want to check your 1/4 inch seam allowances to see if you need to rip any seams out and resew. If you are anywhere near me, I'd be happy to chat and see if I can be of any help.
Happy Quilting