Sophie, keep your head down for a short while but don't fully retreat. Yes you have made a mistake, but nothing can change that. The important thing now is the future - and you can change that. I promise you, people will not be talking about it as much as you think they are. It is really unlikely that anyone will actually confront you, anybody who knows you will more than likely show support and compassion. If anyone does say something, just agree with them and say how ashamed and remorseful you are - there is nothing that takes the wind out the sails of someone who is being confrontational more than agreeing with them!
As I say, the future is up to you. You can either go down the path of depression and anxiety and self loathing, or you can accept your misgivings and learn and grow. I would suggest looking at something called Cognitive Behavioural Therapy or CBT. Speak to your GP, or look for private sessions. You can also get books on it from Amazon. It is all about changing how you think of things, not dwelling on the past and looking at the here and now. It has turned my life around and I now find I am less self critical about the decisions I made in the past, but conscious of the decisions I make now.
I know it is really tough for you at the moment but you can, and will, turn it around.