You really should not have done this. You are too young. She could be had up for child molestaton. What if she had been made pregnant. That would have meant both young lives ruined. Wait until you get married before you have sex. You feel gloomy because that is your conscience telling you what you did was wrong. It might be a good idea to repent, ask God for forgivness and ask Him for His help to keep you out of temptations way. I know it can be difficult but there would be trouble ahead. God loves you