I just started quilting and so far I've made a table runner, a baby quilt and I'm working on my first quilt "of size", it's almost a queen size. If I was following a pattern or something that I wanted to be exact I would probably be in the same boat as you. I decided though that to start out I would just wing things. I designed my own patterns, cut my own fabric and don't really bother with size. For this queen size quilt I just used nine different prints and the one I had the least of that's how much I cut of the rest. It turned out to be almost queen size. I'm not a great cutter, measurer, or sewer, (sew-er not sewer... lol) yet but I thought that if I work on things that I could get away with having seams that don't line up squares that aren't quite square I can work on getting my skills better first and then the rest will come. And sure enough I'm getting better. Sometimes I think I'm getting worse but it's really a learning process. Please don't get discouraged. Try not to focus on perfection and just call all this early work 'practice'. Soon you will be looking back and it will all have paid off.