My male teacher saw me naked!!!?

A few days ago I stayed late at school for a private swim lesson because I have a huge competition coming up. I was the last one there and after showering I was standing naked in front of the mirror (this was in the girls locker room, obviously) brushing my hair (otherwise I get really bad knots, but anyway, its not important). My male gym teacher was locking up the locker rooms and he came in to see if anyone was still in the girls room. So....I was totally naked, without a towel or anything and I spun around to face him when I heard someone come in. I didn't even cover myself up with my hands and I'm pretty developed (I'm 15). I just kept apoligzing for like, a minute, I don't even know why and he said it was fine, don't worry, but he didn't look away and I ran into a stall. I stayed home for one day, when i came back to school my friend told me to act like nothing happened. So, we had gym and I tried not to act weird but when I saw my teacher he winked at me and looked my up and down. He kind of gave me this look, like he liked what he saw? I also caught him staring at my chest while running durring cl! I don't know, but I'm absolutely mortified and embarred. I feel kind of nervous and ashamed, I honestly feel like crying I don't know what to do! Can anyone, please please give me some advice, because I'm so confused right now and I don't now how to face him again!