Yes, there are certainly instances where insecurity has played a role in someone’s rejection. You are not alone. It is always best to work on yourself so that you are as confident in who you are as you can be prior to attempting to get back into the dating scene.
Many people make the mistake of dating when they still feel insecure about themselves and those relationships never last.
Don’t feel bad for turning the person down. If anything, you did them a favor in not letting them get into a relationship with someone who has deep insecurities.
Work on fixing the insecurities that you believe are the most troublesome and you will come out the other side a much more attractive candidate for someone to date.