I feel for you. You were clearly capable of getting a first and unfortunately you might not have. It is completely fine for you to feel upset or anxious. I don't really understand what other people are saying though...you are allowed to feel upset about anything. So if I broke my leg today, I shouldn't be upset because someone else may have cancer? Dumb af.
Also, you shouldn't have felt obligated to give justification for feeling bad about a grade. As we can see your life has been hard but people shouldn't complain that you only previously explained 5%of the story. It doesn't matter.What matters is the fact that you've overcome this to do so well in uni,even if it might not be the grade you want.
Tbh, you're quite an inspiration. But I apologise for the fact that you felt that you had to justify your feelings.