My confidence is pretty high that I would get my *** kicked, but I would inflict some damage.
This is severly under rated. Severely.
I was 5'1 and 90lbs in 9th grade. After the first month I hardly ever had problems. Why? It was not that I was some mastermind when it came to fighting. I lost a good share of fights. The secret is to be more trouble than they want to deal with. Some of the guys that messed with me stopped because even though they didn't like me and knew they could take me, they knew it would hurt them to do so and it was not worth it to them.
It also changes the chances of other fights. They picked on my friends and they knew they had to fight my friend and I, not just my friend. I never, ever stayed out of the fight. My friends knew I could be counted on. 80(ish)% of the time the bully/instigator would back down.