8700 RPM from an O.S. .46? That's really, really LOW. Something ain't right with the engine. Also, NEVER take off with a tailwind, even only 2-3 MPH. It DOES make a difference.
Another thought. "There are old pilots. There are bold pilots. There are no old, bold pilots." You've just soloed; you don't yet have the experience to "feel brave". Take it slow; crawl, then walk, then run.
Dr.1