Girlfriend Owes Me Money!!$$$?

So its not a big deal i just wanted some insight on what other people think. So today i went over to my girlfriends house took her a present....etc. As she was leaving for school i asked her if she finished all her math as it is due tonight, she said no and that she would pay me $20 to finish her her last 3 sections. I said no how about you just pay me what you owe me which is $7 and I'll do it for that, she loses nothing and i get the money i lent her for the gas we we're supposed to split for an unnecessary trip. ( We're fighting by the way lol 😩) I'm not trying to be a dick or anything its just she always says she'll pay me back. So everytime i lend her small amounts I'll never see it back which honestly its not a big of deal its just that sometimes we go out and I'm not trying to spend money at all besides gas and food and i lose out on some. I do buy her things take her out and treat her to things, we've been going out for almost 4 years i feel its been long enough i can ask for my money back. What do you guys think?