Am I wrong to be annoyed at my boyfriends mum? And how to I approach the situation.?

My boyfriends parents and I decided to throw him a surprise party for his birthday. Before organising we agreed that they would cover renting the hall and food, then I would cover the DJ, sweets and decorations. All in all I spent just over £300 on this party (which is fine as a budgeted). However his mum over... show more My boyfriends parents and I decided to throw him a surprise party for his birthday. Before organising we agreed that they would cover renting the hall and food, then I would cover the DJ, sweets and decorations.
All in all I spent just over £300 on this party (which is fine as a budgeted). However his mum over spent on her part and is now asking for half the money that she spent back from me (this will be around £210).
I can’t afford that, I am a student who works part time along with attending uni and it would really set me back on my rent. Not only this I’m a little annoyed that she’s asking for all this money despite us agreeing on what we were covering before the party. I also think it’s unfair that I’m being expected to pay the same amount as them when I work part time and they have two full time salaries between them.
Am I being too dramatic by being upset and annoyed? If not how to I approach the situation? I don’t want any hard feelings or awkwardness and do not want to involve my boyfriend. :)
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