GUYS! I need your opinion and advice if you can:)?

So I had a thing with this guy . After a while I kinda stopped liking him but he still REALLY likes me. We went to a movie and I didn't intend on making out with him but he asked if I wante to so we did. I just did it for the experience and it was fun:) haha do you think this was wrong for me to do? Because now he thinks I really like him and is planning to ask me out.. Advice on what I'm suppose to do to let him down because by best friend thinks that was a b*tch move but I don't think it was a big deal? Thanks for the help:) and we are both 15 if that helps..