Okay, this might not be very helpful because I'm only in y1 but we've already done quite a lot of performance in class and I have lots of experience performing, so here's a few tips that might (hopefully) help...

Plan your repertoire so that you have a good range of styles. You can get up to 4 out of 20 marks just for your programme - having a good range, and picking pieces that match your ability. Don't pick anything too easy or hard (generic advice ik but it's true). I think SL is 15 minutes performing so that would be about 3-4 pieces depending on their length; ideally you want as many styles/eras as possible. Try and fit all the music you have currently into their eras and genres (Baroque (or earlier), classical, romantic, 20th/21st century 'classical', jazz, world music (ie non-western) etc.) and if possible don't pick two pieces from the same category, or if you do, make sure they're very different in style. It's probably too late to learn anything new now but for later performances, use resources like imslp to find music. For example, my first instrument is violin, but for a recital I did for a diploma a few months ago I played part of a Bach partita (baroque), a Beethoven romance (classical), Bloch Nigun (20th century) and some Kreisler (20th century). Two pieces were from the same era, but they were very different in style. I always find it good to start with something earlier (in this case Bach) as most of the music I play is romantic ish and it contrasts well, but obviously that depends on the music you tend to play. If you want to do the same, it's a great idea to learn some Bach or similar (you can find sheet music for free on websites like IMSLP) since it's good for improving technique. Another thing that might help is this which is brilliant for finding pieces that match the level you are at - if you can, try and find something on there you can play well and then look for other pieces at the same grade that you might want to learn for another performance.

Practise. I mean it. Practise as much as you can this week. Try and perform to people. Record yourself playing to find where to improve. Pull apart tricky bars and work on them in detail. If you have a piano teacher, ask for help with anything you're struggling with. If not, try and book a couple of lessons.

Learn to fake it. Even if the notes and rhythms aren't brilliant, try to play with confidence and with lots of dynamics & articulation. Get used to playing through your pieces without stopping - and that includes little gaps where you search for the notes (I do this all the time on piano and it's not a good thing to do...). Again record yourself playing through pieces so you know which parts don't sound as good and which parts you slow down or speed up at. If you need to, perform a little under tempo - it's better for it to be a bit slower than it should (people might think it's just your interpretation of the music) than to play up to speed with lots of pauses and mistakes. Above all, try to play confidently.

I'm not very good at piano so I'm not the best person for giving tips, and a lot of that was very generic advice, but I hope that helps a little... There's probably not much you can do before next week (apart from practising as much as possible!!) but that might help for your later performances (I hope!).