The Greek word for "disciple" means "a learner," and indicates "learning by endeavor" or what we would be "on-the-job training." Jesus said in John 8:31, "If ye continue in my word, then are ye my disciples indeed." Anyone who meets this condition is Jesus' disciple.
"Jailhouse religion," where a person is only sorry he got caught and is trying to get out of a bad situation, will not produce true discipleship. It takes a forsaking of all to be Jesus' disciple. Jesus wants us to "count the cost." It is definitely a commitment.
What the Lord has started in you, He will also continue and complete. That is not to say that your success will be automatic; we have to cooperate with what God is wanting to do in our lives. Our faithfulness may always be suspect, but God's faithfulness is never in question. It is always God's will to continue and complete the good work He began in us.