This happened to my old SO, seriously almost to the letter. I can understand how sinking this feeling must be.
The first thing I want to tell you is that the people that love you do so regardless of whether you are a doctor or earning $9 an hour, and I mean that. My ex and I aren't even that close anymore, outside of sending each other Spongebob memes, but thinking that she has the same feelings as you just makes me want to hug her and tell her that nobody cares how successful she is, and that we all love her.
That being said, I know you're tired of the "it's never too late" speech, but you legitimately have a choice to make right now about what your life is going to be.
I have nearly irrecoverably destroyed my academic/professional career more times than I would like to count - expelled from high school, picked an awful university for all the wrong reasons that I ended up hating, transferred universities for the above-mentioned SO, after tons of hard work received an incredibly competitive internship that I totally fucked up nearly ruining my reputation with those I knew in the industry, the list goes on.
I've had the sinking feeling before. That feeling that you've fucked up too badly and it's just not worth the effort of climbing back up. But you have to.
You don't have to be a doctor, but you feel like this because you know you're capable of doing more, and you know you're going to hate yourself if at the end of this whole journey you look back and realize you never fought back and just gave in.
That feeling is going to be so much worse than what you are feeling now. You cannot let that happen. Like you said, you're smart. Your friends know it, your family knows it, you know it. Orgo just wasn't your thing.
It's up to you now to create a life for yourself that you can be proud of, a life you're excited to take on. It's gonna be tough, especially because every time you fuck up again the sinking feeling will come back and it will be so much easier to just think "ahh if only I would have given up on chemistry," but that's the past. Now you gotta decide is what your move is going forward, how you're going to be happy.
We all love you Sarah, and we all believe in you.