don't worry so much.
i have problems with every quilt i make. i just slow down, figure out where i went wrong, take notes if necessary, then get back on track. sometimes it takes me in a whole new direction that works out better than my original plan.
don't think about the finished size while you're working. cut enough strips and patches for just a few blocks at a time, make those blocks, then repeat the process until you have enough. that way, if you make a mistake, it won't affect the whole quilt and you can recover more easily.
once the quilt is done, the problems don't show. AND i've gained experience for the next one. :wink: