I had a bad past because of my doings in my life, irresponsible, immature, fear, ego which resulted in a great failure. I’ve been training myself how to overcome all this and attain success, and I’m pretty sure things have changed since then. My real problem is I now have an aim in my life, which is hard to achieve, but I’m confident. Still past experiences comes to haunt me, and out of fear I’m scared to do what my mind tells me. I have limited time. I'm not sure what to do.
I thought you were describing my own past at first (“irresponsible, immature, fear, ego…”), but of course it describes all of us at some time, whether in this life or past lives!
There are two specific practices which many people have found to be helpful in letting go of old patterns and attaining success now and in the future. The first one is the pithy advice of Swami Sri Yukteswar:
Forget the past. The vanished lives of all men are dark with many shames. Human conduct is ever unreliable until man is anchored in the Divine. Everything in the future will improve if you are making a spiritual effort now.
We don’t always have complete control over the results, but we can control our efforts. Trust that the changes you have made in yourself are real and will inevitably produce positive results.
The other practice is nishkam karma, or action without attachment to the results of those actions. When we live in fear and tension regarding the results of our actions, it restricts our ability to act with full freedom, energy, and joy. Give the results to God, and trust that positive actions now will inevitably produce positive results at some point. In fact, the very effort to act in positive ways has already produced some positive changes in you. The rest will come naturally in time.