I promised my friends I would meet them for lunch, and I did not keep my promise. They'll get over right?
Why didn't you keep your promise?
I know how bad breaking a promise is. But I had other stuff to do.
It's wrong to not uphold a promise made to your friends since friends are expected to keep their promises and look out for the well-being of each other. If you had other things to do you should have let your friends know and rescheduled the lunch meeting for a better time. Breaking promises is a sign of being a flake and your friendship with your friends will suffer if they know that you cannot be trusted to keep your promises.
Am I a flake? I never wanted that to happen.
I can tell you regret skipping the lunch. Give them a call and apologize. They'll probably forgive you.