Interview!

I was called yesterday for an interview.  So this morning I interviewed and at the end I asked when they were going to decide who to hire.  The principal said in about 20 mins. after you leave!  There was another teacher who had put in for a transfer to this position as well but when they called to schedule an interview, she decided to withdraw her application.  So it was just me!  I wish I would of know this before, I may not of been so nervous!  I am assuming I am going to be offered the position but it has been almost 6 hours since my interview and I haven't heard anything!  Should I be nervous?  Should I just assume human resources is busy and just hasn't called me?  I feel like I shouldn't assume anything so I am just on pins and needles waiting!  I will keep you posted!