My ex said “I’m scared I made the wrong decision”

My ex broke up with me 2 days ago, we only knew each other for 4 months, her reason for it was because she didn’t feel like we were clicking and we lost the “spark”, she said it was there before but not anymore, and didn’t know if we could bring it back. When we were talking about it I kind of shut down and just went along with it, I wish I would’ve said something to try and fix it but it seemed like she wanted it to end it and she asked what I thought and I just agreed and said maybe we’re not meant for each other. Now I really regret not fighting for what I wanted. And then yesterday she told me she was scared she made the wrong decision. So I really don’t know what to do