I understand your pain, it was opportunistic betrayal.
You likely have a low self worth issue and need for validation (as your mutual friend, that makes the pain deeper, as it wasn't just enough).
Okay, you messed up, is good you told immediately, you took accountability, is an important step, it means you do not only feel shame but guilt.
Without guilt no Reconciliation is possible.
In this moment she will be hurting a lot, is in the shock phase, it will get worse, much worse, so you will have a challenge ahead, considering what happened and that she needs your care because the baby.
You need to try to care for her physical well being. It will be hard as she starts along the path of betrayal trauma, but is the right thing to do. Listen to her, no matter how it hurts, your decision hurted more, she needs to see that you "might" still be a safe partner even if you choose to betray her.
Now read about WS guide.
You can read around the BS posts to understand what expects her and you from down here. The rollearcoaster started, it cannot be stopped, but is not said the final word until it is over.
Be aware that the wound is very deep, who did not suffer it can hardly understand it, trust me, you do not want to ever experience it, is worse than being shot or seriously harmed physically.
You are hurting and that is true as well. It is a good thing, it will help you to grow from this and never relapse on betrayal (if you put the work and resolve the issues).
Mind that she might go either way with your relationship from here on. That mean split or give the chance of R (is not automatic, R requires the BS to keep the pain of betrayal and try to heal the bond instead of running away and healing themselves).
Do not expect a second chance is due, because it is not, but your threading now when she needs the most can help her see through her decision the moment that she will have room to think it over when the hurt and grief stabiizes just enough to give her few moments of break from the pain.
No grand gestures, consistency and respect. I wish you both well.