IMHO, you don't have a relationship until you are together in person. You are not going steady like when you were in middle school when you are 21.

Do you feel any physical attraction to him? If not, tell him you really only feel a strong friendship and you were too impulsive a week ago, no big mistake was made.

If you feel a bit of attraction, make plans to get together in person and see how it goes. That's how a relationship forms. You don't just decide you are in a relationship. You spend time together and feelings and experiences bond you together over time.