I feel like my friends are just using me because of what I do. :(?

I've been baking for almost a year now, and I would always bring little sweets to school, like brownies, or mini cupcakes, just for fun. But now it's just really pissing me off. My friends are always asking me "Soo, can you bake me ___?" And I'm just like....I just kinda blow it off, like "Eeh, well..." because I can't say no. I hate saying no, because I feel if I do, my friends will hate me, and I don't want that to happen. But I can't convince myself that I shouldn't care what ppl think. Anyway, so my "friends" are like "You gonna bake me something for my birthday?" or just stuff like that, and I'm thinking "And what the hell are you gonna get me for my birthday, thinkin about yoself" And it's like ppl I don't even know that well asking me to bake them something for their birthday!, or my friends will tell me if I'm baking something for one of their friends (which most of the time I don't even know that well) that I need to bring enough for everyone. I've told them that the stuff to bake these things doesn't come falling out of my ***. This stuff costs money, and they just think that it's so simple like "OH I GOT EVERYTHING LET ME GO BACK THIS". No it doesnt work like that.. Then the other day was one of my friend's friend's birthday, and my friend was like "So, you need to bake something for Lindsey's birthday, and when you do, you need to bring enough for EVERYBODY, ok?" And I straight up told her "You got the supplies" nothing followed. The next day, I saw them sitting together and they was like like "Elizabeth, you got the stuff?" I was like "Uuh, no?" "Why not" "Becuz stuff cost money, and I aint got none". (End the conversation.) I feel as if they just like me for my baking, or they act like I'ma machine, and they just think that I'm gonna bake them whatever the hell they want. I don't think so. I sometimes wish I hadn't even started baking, but I can't stop, I enjoy it so much. What do I do about this? My friends are acting like complete s, and I'm not taking this bs from them anymore.