Which Position?

I've never played orgenized football before, but im starting this fall and I want to know which position to work on. Im starting 6th grade. Im about 5ft tall and around 95lbs. I am really quick and fast I have good hands, but I really enjoy playing running back. On defence I am sorta good at tackling, but im a good at covering. I went to the McKinney Boyd football camp and was good at pretty much everything except off. def. line. What should I train???