Hi there!! I'm Alma, I got a 9 for art in my GCSEs, hope I can give some good advice
I did AQA Art, Craft, and Design, but I'll just talk about idea development which I'm sure is similar between the two. From what I'm hearing you're concerned about how to develop your idea of running going forward. I totally understand, especially at this point of year, getting worried about where you'll go next with your ideas. Most of all, I'd like to say that not knowing what you'll make for the exam 2 months before it happens is a very good thing. Your ideas and exploration is what gets you there, if you're doing good exploration of ideas and letting them influence your work, its impossible to know how your work will have been shaped in 2 months time.
If you're hitting a brick wall and feeling limited in your direction, start with whatever idea you're on right now and see just how abstract from that idea you can go. So take running, and for example, you could focus on journeys and destinations, bring that into places and do small experimental pieces on landscapes. You say gatherings, focus on holidays, travel to holidays, long distances, loneliness and isolation. Maybe go more conceptual, use the idea of running symbolically, then you can venture into fears, expectations, what people run from in their daily modern lives, the 'daily modern sprint to survive'. Cavemen and their running for survival, the office worker running for their bus.
When projects start to feel limiting, let whatever idea string you've got that's not sparking joy take a seat and explore other stems of ideas. Examiners love it when you explore literally every idea that comes to mind even if its suuuper loosely connected, and even if you don't like the idea and don't expand upon it, that's part of the process. Dedicate a page or two to a specific subject of drawing, a media, a super out of character artstyle. If you totally hate it, drop it, pick up a new idea. Even better if you dip back into your own experimental work later down the line, lets say you like a particular media or theme you briefly dived into months ago, you can pick it up and revamp it.
Using lots of media is great, especially experimentally and earlier on, now I'd say focus on your ideas and use the techniques (like you say, your graphite and gestural markmaking, very very good, and your observational drawing and photography) as tools within the exploration of your new ideas. Wherever possible, anchor your new ideas down with an artist. Explore, research, refine, move forward.
The one thing that will ensure your doing well in a subject is a real love for it, don't bog yourself down in a string of ideas that makes you feel too limited or uninspired. If running isn't doing it for you, don't be afraid to dip in and out of it. I started my Externally Set Assignment dead set on illustration of story books, ended up making a diorama sculpture of an animal in my exam, that I only got to the idea of a week or two before the exam. If you know what you're going to make in your final exam 2 months before it happens, your exploration of ideas is not gonna be adequate, so not knowing where you're going to go is a very good sign as far as im concerned.
So above all, DO WHAT YOU ENJOY, don't plan too far ahead, follow your idea journey literally anywhere you like that you can defend as 'gatherings', and work that mark scheme! Good luck!!! If you have any more questions I'd be very happy to help however I can
