i need friendship advice

Hey guys, so i have been friends with this girl since i was six. I am now 17 and we are close friends. The last couple of years we're not as close anymore because we both hangout with different people. Around two weeks ago she asked me if i could do her college application essay. She does not speak english and the essay has to be in english. So i said i'd do it but she has to buy me a cake. I asked for that cake a bit jokingly but i actually mean it. Not because i don't want to write the essay for free or something, but just to have a little fun with things. Now the essay is done and i gave it to her.

When i asked for the cake like she promised l, she said it was to expensive and told me to pock something else. I know she's not in some kind of financial situation, she's pretty well off. The price of the cake is about the price of 2 medium sized starbucks drink or less. She never mentions "paying me back" and just waits for me to ask for it. She acts annoyed when i mention it too.

I did the task for her with good intentions bc i want to help her, i put so much effort into making it good bc its important for her. The way she is acting is really pissing me off. I feel used and tricked. Like you can't at least be thankful?

Should i tell her how i feel? It truly does bother me.