Sorry this happened to you, OP - it sounds awful.
I would do what PPs have advised and have a debrief with the medical team.
Before I meet with the medical team, I'd also:
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do my own thorough research on your actual condition and the recommended diagnostic procedure for both conditions to get it clear in my head as to what they could/should have done differently and/or what would have been done differently in the NHS, and
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call a couple of reputable personal injury lawyers to get an idea of whether it sounds like you have cause for a claim - the reason is do this first is because it might influence how you handle the debrief (in terms of whether it ends up being more about closure or fact-finding).
My DD had a misdiagnosis as a baby that was hugely detrimental to her, and now she's older (still young enough to sue if she wanted to), she's gone through phases where she's wanted to sue her drs as their misdiagnosis still affects her, and I've looked into suing them in the past too.
At the moment we've concluded that actually, we think the surgeons probably did the best they could with the available information they had at the time (she had a rare condition but they assumed it was something far more common, unfortunately to her long-term detriment). I was very angry about it when she was younger, and it obviously still bothers me, but I'm glad I waited till she was older to see how things panned out and so she could make her own decision. And I've definitely mellowed over the whole thing over time, too (although I'll obviously support her 100% if she does decide to sue over the next few years).
Obviously, your situation is different as you don't have the luxury of waiting two decades before deciding whether to sue. But you still have 3 years (from the alleged negligence), so I'd advise you to take some time before deciding, as you might find that having to relive the whole horrible experience again and again adds too much additional stress to your life on top of everything else you're going through.
I'd also suggest you get some counselling - even if you don't sue them, the hospital should at least be covering that cost! Don't waive your right to make any claim in the future, though.