In trading - as in life - there is a lot of space for regret, because it's inevitable - after we know the result - to blame ourselves about the decisions we took or we didn't take.
But it's completely useless: you took some decisions with the data at your disposal, and it was what you thought it was the better decision.
That's all.
All you can do is to take a better decision next time: there are still a lot of trains...