Don't let yourself get discouraged. this is not what I would call a beginner's quilt. Yours is really a good quilt.
Are you aware of pin matching? That's where you pin through the intended seam connection point then pin on either side of that and remove the original pin so it won't distort things. Of course, I can't tell from here, but when I had cut off points like that, a part of the problem was inaccurate seam allowances.