I am in a bit of a similar situation. I was really annoyed with one of my results as I missed my offer for pharmacy as I got a C in chemistry but then eventually got accepted into my 1st choice due to extenuating circumstances- like you I am very disappointed and was considering retaking the year but then thought that I have the opportunity to go to the university of my choice, and I dont want to get bogged down in retaking the year when it was, like you partially due to personal circumstances.
The past is the past and as long as you know that in your heart you could have done better, if that gives you the drive to work really hard at university then go for it. I believe that sometimes you just have to move on- for me it is certainly going to make me work much harder and buck up my game and also to start a new life away from an unhealthy personal situation.
For most once you have got to university your A-level grades matter less, and if they are vital for a job application then you can always do them at night school. The most important things are drive, enthusiasm, determination and experience. Do what you feel you need to in your heart but dont be disheartened by your results- use them as a learning curve. Remember you've got into the uni you wanted to go to. Hope thats helped a bit. Good luck