Got a bit ahead of yourself there, did you?
Well, unless you've got something that's going to accelerate the
growth of your hair, there's not a whole lot you can do about it,
is there?
Just turn up and don't say anything about it. If you do get crap
from the instructors about it, just grin and bear it. Trying to
defend getting the haircut is only going to get you marked as a
gobby smartarse. Take it with good grace and you may earn yourself
a bit of respect.