This is probably a really dumb DIY question... Apologies in advance!

I hung a fire door about 4 weeks ago and haven't got around to varnishing
it. Its on a soundproof booth I've built inside my garage so I was eager to
get it a really snug fit. Its now expanded so it wont close properly. Can I
do anything to get it back to the good fit again without shaving more wood
off? I've put a dehumidifier in there for the past week but it doesn't seem
to have made a difference. I don't want to cut the door down further because
if it shrinks back again the gaps will be too big. Any ideas?!

Cheers

James