can’t finish exams - Creative Writing - OCR English Language GCSE

hi, first time posting here, sorry for any mistakes etc

I have a lot of problems with finishing the creative writing section of paper 2 on the gcse English language exam - you get two options of either a story based off a title they give you or a bit of autobiographical writing about a given topic.

In my mocks I got a low mark (quarter marks) because I only wrote about 85 words across a paragraph and a half in the half an hour I had to do it, and didn’t get very far into my narrative. That was on a really bad day, and if I give myself 45 minutes (including planning) I can write roughly 200 words across 3 paragraphs, based off of the practice thing I just did. That’s about the 2nd stage of a 5 stage plan I had, which is an improvement but not enough. I’ve also pretty much run out of practice papers for my exam board (ocr) though there are a couple in my revision guide I think.

How can I write enough to finish a story but without sacrificing marks on techniques and content?

I’m allowed a word processor in exams, and rest breaks (you can take any number of breaks up to 30mins total but have to close your test booklet), but my school won’t allow me extra time. I’m getting high grades in nearly all my other exam subjects at least (don’t take any other essay ones except English lit). I think my problem is I just don’t think fast enough to put down words and sentences, or I’m just too careful with how I choose them (but if I’m not then I would sacrifice quality lol).

Any advice really appreciated, thanks for reading