Hey man,

you're probably fine. I don't know the details, but humans are fallible. you're only human. friends should know this, they're only human too. I doubt these friends have all been perfect all the time, and I doubt they'll do everything perfect from here on out.

If it caused a problem, tell them the truth. you double booked. you had to pick one over the other. you feel bad you flaked. you don't intend to make it a habit.

if it cost people something, consider making it up somehow. but I would propose that unless it's cost them real bad, good friends ought to accept the apology without expecting the compensation. they'll mess up someday too, and it's better for everyone to be kind.

don't hate yourself. it does no good for anyone. counterproductive and undeserved. develop a system to help you. you can't always change your nature, but you can build around it.