I'm sure it's a urine test. Hair tests are expensive, and I doubt any school would be willing to shell out the extra cash, when urine tests are so cheap.
Personally, I've never heard of anyone having to have their hair tested, expect for those applying to police forces or government jobs.
You can buy a THC urine testing kit at any drug store for under $20. 36 hours is a pretty big window to take a drug test - many drugs are out of your system naturally in that much time! Geez.
Cross your fingers, take this as a lesson, and don't make the same mistake again.