I've felt the same way you have, but then after much encouragement, talking with friends and mentors and scripture reading, I realized that I can't change what's happened in the past. Our time on earth is so short and God will continue the good work that is in us. We just have to heed the call. Stay focused on Him and all the other things he has in store for you will come. Don't beat yourself up over what may have happened, but stay focused on what is in the future.