You know, I have thought deeply about this question. We all have regrets and mistakes that we have made that we wish that we could go back and have a redo. I sure have many of those.
However, I have come to realise that all of those choices, mistakes, and triumphs make me who I am right now. Without any one of them I might not have the insight that I have, or possibly be able to cope with the set of cirucmstances of my life.
I wish I would have taken better care of my body. I wish I would have laughed more. I wish in my teens I would have allowed myself to be a teen and dye my hair purple and do outrageous things.
Alas, the only time I can control is my now. Its doubtful I can actually control now, I can simply choose to shape my perception of events and I can choose to be happy.