don't worry about the door being not shut its not a big one. Its certainly not worth going off the end of the runway because of.
Just ignore it and get up to cruise height and open the top catch and then open the door catch and give it a pull and it will more than likely shut and then shut the top catch. If its still open a bit don't worry about it the slip stream will keep it shut.
Some instructors myself included when its hot open them anyway on purpose in flight.