MY DAD IS STALKING ME ONLINE! NEED HELP FAST?

Alright I do Florida Virtual School and I had to email my teacher something and a little yahoo messenger thingy popped up and it was my dad and he was like "Why are you online", "What are you doing" and I was really creeped out because I don't see my dad much and I don't really get along with him cause he hits my stepmom and sister and now im scared he can see me! WTF SHOULD I DO? I logged off of yahoo messenger can he see that I did that? Is he gonna be mad? OH CRAP