I think for next time, you need to concentrate on 2 things - keeping the wrist still and using the arm to make the strokes, which helps keep the correct angle, and applying just enough pressure to get the blade cutting. If you watch mantic59s videos, especially the general DE shaving guide ones, he refers to locking the wrist - watch what he does, but don't try to lock the wrist, as you'll grip the razor too firmly. You need to hold it just firmly enough to maintain the angle, but not so firmly that you apply too much pressure. If you use fountain pens it's not dissimilar - a gentle but secure grip.