Hi and welcome to the QB. If your strip pieced blocks are coming up 1/2 short that is quite a bit more than would be taken up by pressing. First double check are your strips cut correctly at 1 1/2"? Measure your center strip in the pieced block it should measure 1" finished and your two side strips should measure 1 1/4" each in the unfinished strip set block. If it does not you need to work on your 1/4" seam allowance, it sounds like it is too large so you will need to make adjustments. You may need to sew a scant 1/4". How thick is your thread? Thread can take up room in a seam allowance, especially a very heavy 100% cotton like a 40 wt 3 ply.