How to overcome changing undergrad course/university due to failure
Difficult times occur. This is normal. Unless you did something foolish that caused your failure (and nothing indicates you did), there is no reason to feel regret. 

You cannot control everything in your life. Whoever does not attempt anything, does not fail; people of action fail regularly. Failure is a central part of life, and there is no reason to regret attempting to study physics and then finding out it's not for you at this phase of your life. In fact, I actually recommend testing ones limits early, and knowing where they are makes one a more mature personality. Your current success is point-in-case.

And, keep in mind: limits may be expanded, albeit slowly. Therefore, my recommendation depends on whether your regret refers to ceasing to do physics itself (the topic!), or it is rather the failure to complete (the studies!) that you regret. 

If you feel that you would have liked to do physics (the topic!) after all, perhaps you can consider reactivating your studies (or add a Master's degree as suggested elsewhere). But if it is only the missed opportunity, then I recommend to notch your physics studies up as valuable experience and move on the path where you have made progress and which clearly suits you well.