How do I deal with the fact that I have made a wrong decision in my life, which could potentially ruin my future and end my career?

There is not a single living human being who took all right decisions in his life and can say that he is living his life like a king.  Its natural, its permissible and its right that you have taken wrong decisions - so long you look at them as wrong and so long you try to look at one side of the problem and so long you refused to find a solution for that wrong decision. For every problem  for every issue and for every decision there is always a second or third or fourth way of going out of that issue.  Because we have been blinded by the excessive light of that decision we are unable  to see beyond that decision we have taken or the decision we have taken and went wrong - this issue has blinded us to an extent. Sit down, make an analysis and go back to the situation where and when you were yet to take that decision and verify what were alternatives you  had at that time and come back and verify about what are the alternatives you have now. A mistake can not ruin your life - whether it is connected to finance or woman or change of profession.  All decisions can be repaired, we need only the vision, equipment and patience and capacity to listen others.

To find if you are really making mistakes , get feedback about yourself from others. If you find that your feedback is not satisfactory and ensure that you are making a mistake , you must surely take a step to change yourself.

"You die, she dies, everybody dies." - Heavy Metal, the movie. A human being is an ape-like animal that builds a model of the universe in its head until physical maturity, whereupon that human moves its ego inside the model and avoids the real universe at all costs. You just got smacked by the real universe. It's up to you to explore and employ that connection to become more than the people who never touch it for fear of "ruining" some artificial idea of life (or afterlife). People do stuff. They have reasons for doing stuff: in that order. The religious answer is to forgive those who trespass against us, but don't forget to forgive yourself and go on as well as you can, knowing that life is more random than everyone believes it to be.

How you deal with your error depends on the type of error, where it was committed, and who, if anyone, was harmed by your actions. If you can apologize, do so. If you can perform some act of restitution, do it. However, mistakes involving your job can be a bit more difficult to resolve. If your job may be threatened, you'll need to think about all of the possible ramifications. In your shoes, and depending on the decision, I'd start looking for a new job, just in case. If I had a little time before my error became apparent, I'd ask for letters of recommendation from coworkers or an immediate supervisor. In fact, I might go ahead and write that letter, leaving the signature line blank, then have  someone sign it, if they agreed with the letter's finer points. In other words, I'd try to get ahead of any blow-back, before it happens. I hope these suggestions are helpful. Good Luck!