few comments:
the B could just be like the 8, it would look OK. You could also make it sort of implode, like this:
__
|_/
|_\

The C would look just fine if you made it square.
the Y, too.
You don't have the right display tiles to make punctuation, so don't put it there. It looks cleaner.
If you could work out a display that had a middle line through it, your letters would have more potential.