I will stop feeling like a failure when I have reason to believe I am not
When things go wrong, you can't feel like a failure. You need to use it to motivate you more. In medical school, surgeons and nurses will treat you like CRAP. You will feel horrible. You, as a med school student, aren't useful and only impede efficiency there. You're nothing but a nuisance and the personalities there will treat you like utter crap.
If you keep going through this mindset, I'm going to have to beg you to never apply to med school. Not only will you be pushed into the biggest whirlpool of depression ever because of your self defeating mindset, you will not make a good doctor.
What if a procedure didn't go well and your patient suffered from it and I'm next to be operated. I sure as hell wouldn't want you to operate on me, knowing that the failure of the last operation will be of detriment to your focus and attention.
Okay, if you're not in it for the prestige (which I now find it easier to believe since you now demonstrate flexibility in your choices), you're definitely don't have the right mindset.
And now, to answer your question, yes you can still redeem yourself but the path is hard. They don't want to make it easy for slackers to get into med school and become a doctor. Since you're a slacker, you will need to prove that you aren't.
But in the end, just because you don't achieve your "dream career" doesn't mean you're a failure or that you won't be happy. In fact, I'm sure being a doctor isn't cut out for you. You just lack the drive to. When you fail, you feel depress and aren't motivated to work harder. This is the exact opposite of what a doctor should do.
Having a good attitude without having a good reason too is like trying to start a car with no engine. Sure you may be "positive" and "have a good attitude" while you further your attempts to get the car started. However, ultimately it will never start without an engine.
No, having a good attitude, no matter what, is like attempting to start a car. If it has no engine, you try and fix that problem. Call someone to attach/fix the engine or buy a new car. Having a bad attitude in times of trouble is like not even wanting to drive, no matter what.
If you can obtain this mindset and change your way of thinking, then you will be more ready to take on the challenges to become a doctor. It's going to take time to change this way of thinking, though.
What do I recommend you do now?
Postpone your plans of becoming a doctor and work on your life and attitude right now. Find other jobs that can still carry your passion(whatever it may be). You're not ready to be a doctor yet.