Be patient. If this is only your fourth shave you're doing pretty well. Technique is everything. Just keep at it paying attention to no pressure, blade angle and grain direction.
Also, BBS is not really what you should be shooting for. You should be shooting for an irritation free shave. BBS just sort of happens but its not what your goal should be.
It may take a few months before you're getting consistently great shaves. You'll have days between now and then where things just aren't falling into place. Don't get discouraged.
TOFLAC-U, AOM, LEMS/ Stay back! I have a Merkur, and I know how to use it!