My degree result was far below my intellectual capabilities. Even despite that, I could, in theory, have achieved great things in almost any career I could have chosen. I have a natural aptitude for understanding complex ideas and systems very quickly, am capable of being highly organised, am a creative problem solver and have a very high IQ.
But I suffer ADHD and occasionally crippling social anxiety, and there's plenty of reasons to suspect that I'm autistic. I also have a family history of severe psychosis and suicide.
So I'm just happy that I've carved out a stable, comfortable life with a wonderful DC, a few good friends, good family relationships and a job I usually enjoy. I've learned to measure my expectations not by what I could have achieved had I been a slightly different version of myself, but rather what I have achieved considering the person I actually am. Given the risk to myself of just being me, the fact that I'm still here as a functioning adult is a victory of sorts.
Are there things I could regret in my past? Yes, there certainly are. I've ruined friendships. I've let myself be manipulated and taken advantage of. I've passed up opportunities for a much more successful life. I've missed out on a lot of fun. But do I regret that I've become someone who tries to get the most out of my particular life, and who tries to be the best person I can hope to be? No, of course not, and that is in part because of the mistakes I've made.
The best approach to life is, in my mind, humility. We are not the masters of our own destiny - that's an idea thrust upon us by our deeply individualistic, selfish, identity-focused society. It's profoundly egotistical to think that we mere mortals can simply choose to be whoever we want to be (and therefore should regret any deviation from that imagined perfect life). That's not how humans work. The best any of us can do is to try to learn from our mistakes, make the most of the hand that fate has dealt us, give what we can of ourselves to others and not let failure deter us from embracing life.
I don't regret the flawed, imperfect, but ultimately positive person I am today, and that makes it a lot easier to not regret the mistakes I've made in the past.
tl:dr
OP, make the best choice you can. If it turns out to be the wrong one, don't beat yourself up about it because making mistakes is part of being human. Try to learn from mistakes, stay positive and stay generous of spirit and you'll have no need for regret because you'll be a good person, and that's the best achievement there is.