Hi! Hope you're well!
I saw this post and it really reminded me of myself at much the same stage that you are at right now. I managed to secure interviews for Slaughters' Vac Scheme and TC but did terribly in both interviews - my fault entirely - but I hope I can give some advice towards what you could do to land that interview call.
Obvious disclaimer, no clue if what I am going to say had any impact on me getting an interview, definitely a case of coincidence and not causation.
My background is that I did decently in my GCSEs, I got 3A*s, 6As and 2 Bs - and I massively screwed up my A levels, I got 2 As but also a D. Lost out on my university offers at Durham and Nottingham and went to a non-Russell group university. It all ends well, I'm now doing a masters at Oxford, but back then when all of this happened, it was very doom and gloom.
I got a 2:1 in first year, but every year after I got 70+. At the time of my application to Slaughters, my grades were 80%+. Slaughters definitely places a premium on academics. The other thing I did was own my error. I privately sat an A level (in Law, why make life harder than it needs to be), and easily scored an A with limited study, after all, I'd studied those topics at a much higher level.
Besides academics, I focused a lot on extracurriculars. I focused on those activities that were "unique achievements", so I avoided things that most people could easily do, like take part in societies, etc. I did essay competitions, national level, winning one and being a runner up in another, and mooting competitions (although I did not win any there). I also wrote full research papers for publication in peer reviewed law journals. Any one can write, any one can write a blog post/website entry, not everyone has a peer reviewed publication. There are student law journals in excess in the UK, so you can take advantage of that. These extracurriculars really showed that I was living, breathing, drinking, law and gave me things to talk about and tie to the firm in my cover letter, beyond "I got X grade in Y course which ties to B practice area".
Also I did part-time non-law jobs because I was struggling to feed myself but also for "transferable skills" (Please don't ask me about them, I have no idea how stacking shelves and teaching kids maths somehow ties into mergers and acquisitions). Do the online courses they offer, they are truly dreadful but literally everyone has them, and attend any in-person events you are eligible for.
I think putting all of that together, yes - bad A levels, but owning that mistake and trying to rectify it (which not many do), and then a linear growth in grades through university, winning national law competitions (which ipso facto make me unique), and legal publications in recognised peer reviewed journals (I can think, big brain, see) - must have ticked something that recruiters were looking for and offered me interviews.
Interviews which I completely failed at - they were literally my first ever interviews in law - but where one door closes, another opened, now going to Oxford - so yes, it's great to aim high, even if you fail, you'll have gotten somewhere - rather than nowhere.
Hope that helps, happy to chat more if you'd like.