I remember when I was in year 12 (last year) I was just like, damn, how badly did that girl do in order to retake her year. Hundreds of people retake every year, and of course people will find out about it and probably make a smug comment, but they don't know you or how it happened so they're in no place to judge you. You'll soon and quickly grow to ignore the opinion of other's and focus on yourself.
And then it happened to me, and I retook. I felt so embarrassed that people would be moving on without me and I'd be stuck with girls who were younger than me. But if I'm being completely honest, it was the best decision I've made in terms of education. I could have carried on like a sheep to year 13 despite not being satisfied with my grades and suck it up if I got crap uni offers, or I could have (which i did) retaken my year and get my grades up to scratch, which I have this year
You've got to learn that at the end of the day, you'll be the one who is stuck with yourself so instead of thinking of yourself as "the person who got bad grades and retook", think of yourself as "the person who retook because they knew they could do better, and deserved better in terms of future prospects".
A new girl who retook year 12 at my school was actually very snobby about it.
Lets say we're in a biology lesson. "Ooh ooh I know this, this is so easy, I've done this already"
Or let's say people are worried about a mock , she'd say, "well I already know how to revise because I won't make the same mistakes again, but everyone else will fail"
Don't be like her. But also don't care if they look at you differently because you retake. At least theyll know that a levels are fricken hard compared to gcse.
The only stigma you should really worry about is the one the university attaches to retakes - for example LSE will straight out reject you if you're a retake.
I was a retake, I experienced no stigma, heck I wasn't even ashamed stuff just has to go that way sometimes you know, and stigma is irrelevant to your life; get your grades and go uni that's the sole purpose of sixth form/college.