Just ignore the non constructive people.
Take a step back and realise its done, but it could eb a good thing becayse its alerted you to a situation that you still have some time to do soemthing about.
1. Work out why your grades were so poor. That means talking to your teachers. If you get grades that low it means your answers are very poor, so its going to eb a mix of not having enough knowledge, not understanding the issues or what they want, no constructing answers thats cored marks.
2. Be honest with yourself and work out how much you feel you undestand the subjects, How much revision did you do? You obviously have some idea of what you expected.
3. Depending where you fall on the above then work out a plan as to how you intend to improve things. Is it going to be possible? Are you prepared to do what is needed?
At this late stage its going to be very difficult to get top grades, but then if you ahve Uni place or required grades to get thats the target.
If you are so far behind where you need to be, then consider talking to your teachers and moving back a year. I know it may seem like it at your age that a year is forever, but it really isnt. Discouraging, but if you apply yourself then its possible to turn things around. You just have to figure out whether you have enough time and ability. Take advice.