Please no overly harsh comments, I have rejection sensitive dysphoria and ADHD

I woke up today and I had the bright idea to look at tickets because I felt like travelling (I’m broke by the way, but just search things like this a lot out of curiosity).

When I found tickets I could afford I messaged my friends asking if they wanted to go with me for a day trip to the location by train, but they didn’t respond so I messaged my nan. She agreed to go with me and my mum said it would be nice so she booked us both tickets.

But after the ten minutes of “wow a trip would be fun” I then instantly changed my mind. I have two exams determining my university place next week!! I also feel like crying at the idea of going on this trip in two days time but feel I can’t do anything now. My mum was just trying to be nice but the last thing I want is to go. What is the next correct action to take here?

I don’t want to come across as rude, but I’ve been crying for two hours now about this and feel I can’t do anything at all until I can get it out of my mind. I’m incredibly frustrated that this happened and the last time I went on a trip it took two days of crying to get over how overwhelming it was.

Is there even anything I can do? Sorry for venting I feel a bit stupid right now The idea of going fills me with dread and I want this feeling to stop because I’m lying down unable to do anything.

The tickets she bought are totaling over £150…. More money than I have so I can’t offer to pay it back to her in full at once either I am mostly worried about upsetting her and I genuinely don’t know how to approach this (go/not go) so any advice is appreciated

My mum is a lovely person