His friend told him I'm going to say yes to him tomorrow!!! HELP!?

Theres this boy in school that has liked me for a year. Last year he gave me a teddy bear for Valentines and he told my friends that he has got me something really nice for tomorrow. He's really sweet but I only like him as a good friend. Also I'm not aloud a boyfriend, my brother and dad said I'm too young which I agree with (i'm 13). What happened a couple of weeks ago is when I liked him I was texting my friend at lunch saying that I liked him and I wish I could be his girlfriend and later that day he was playing a game on her phone and saw the texts. I was talking to his friend and he was asking me if Zack (the boy you likes me) asked me out to be his girlfriend, not on a date, what would I say? And I knew if I said no he'd tell him and he would be crushed and really sad so I said that I don't know and his friend told him that I like him and would say yes. He keeps texting me now saying 'I can't wait till tomorrow xxxxx'. I feel really bad because I feel like ive been leading him on but I was only being friendly. Help me how to let him down gently tomorrow please?Thanks!