Some people went to do some things today and I wish that I had gone with them.
Is there a reason that you didn't want to go at the time?
I wish I had gone with them today, but maybe it's for the best that I didn't go.
I'm sorry you regret your decision, but there's no longer a point in mulling over it. It happened, and so you have to move on and not think of the what-ifs. Just remember to think harder so you don't have any more regrets.
Having no regrets is a fairytale that doesn't exist.
It's a bummer you changed your mind, but focusing on what already happened is just going to make you feel worse. Just think about how you can go next time and move on.