Sew much good information! I find that I do better if I cut w/rotary cutter and mat than using templates, I cut exactly on the ruler line (use caution at the ends of the cut that you dont move the ruler though). When you press your seams, just press them and do not iron them. The iron stays put, dont slide back and forth, (that will stretch the bias edge every time.) If your squares are still off, that is when I cut a 1-1/2 to 2" strip and sew around the block and then use my size up ruler & make them the exact size I need. Sometimes, that little strip just makes the quilt. (At least thats what I rationalize with myself)
Bottom line, dont give up. Practice will sometimes be frustrating, but the end project will be worth it.