What about relationship certificate? Do I have to make it or not?.

Besides, I had already spend 15 days ( in a conference) in DC, USA in 2005 with B1/B2 visa. . I stayed legally there and returned back after my program was over.  I didn't went back to USA though I had a multiple visa. My visa expired in 2006. Will this be plus point for me for my f-1 visa application now?

Thanks a lot ...........