(someone) blew it
When someone messed up or wasted an opportunity, you can say that they "blew it".
Here are some examples:
I could have talked to her, but I blew it.
I was so close to winning, and I blew it!
You can also tell someone:
This is your last chance. Don't blow it!
This is a casual expression, but it's not rude. You can use it around most people.