Should I reject Oxford?

So on the 14th of Jan, I was really shocked, and delighted to get offered a place to study at Oxford, but I am reconsidering my application.

At the end of last year, I achieved and was thus predicted A*A*A*A*. I then submitted my UCAS application and went through the whole process. In later October/early November, I was in a really dark place (nothing to do with university options). I was deeply depressed and borderline suicidal, and was having these thoughts and feelings while going through the Oxford interviews, and learning loads of important content in my A Levels. Long story short, I fell behind by a lot, due to skipping lessons and a genuine inability to do my homework/classwork.

I did therapy, and a lot of work on the aspects of my life that were fuelling my depression, but completely fell off the rails in terms of school because of this.

These past two weeks, my school held a full set of mocks, and getting the results back today was absolutely shattering. I knew I'd do badly, but I got BCDD which really broke my heart, as I'd been in such a good mental and academic place just months ago.

I'm grappling with the fact that I'm unlikely to meet my offer, which is A*AA, and wondering whether I should reject the offer, or accept it and try to meet the grades even though it is unlikely even if I put in a lot of hard work.

Luckily, I had two spots left on my applications and applied to a BBC and a BCC requirement uni last week, so all is not lost, but I'm so upset

I know this seems like I'm being incredibly ungrateful, but I'm just looking for some advice as I am heartbroken.