400 for a week is a steal. I echo what ZacD, if you are decent at what you do, you are undercharging by a ton. 400 a day is considered a good price in the part of the country I am in.
Edit: just want to say that especially when you are just starting out, yes, it is easy to have doubts about your worth. Rarely will anyone be as critical of your work as you yourself are. It’s something that gets better with time and experience.