Advice?

Okay so my boyfriend and I have been dating for just under a year now (we're 15). We have great chemistry and an amazing connection and I can see myself actually lasting with this guy. So. Then in my PE class, there was a new boy (Ricky) a few weeks ago. Being a decent person, as a team captain I chose him. Great. No biggie. Then a few days later he got my email, he asked for my Snapchat. I ignored it and went on my merry way. Then today in PE he was very VERY obviously hitting on me. I tried to be nice and avoid him but anywhere I went Ricky kept showing up. After class he sent me another email asking if I would add him, to which I responded "I don't have a Snapchat" he then asked what I did have. I haven't responded yet. I know this is a very high school typical problem but I just need some advice on how to tell Ricky to back off without being rude. Thanks.