RPR at 6 weeks may be wrong, but a T. Pallidum specific test at 10 weeks is highly reliable: syphilis can be ruled out.
A chancre on a tongue is an uncommon thing among various oral ulcerations and pictures on the Internet may be very confusing. Trust the tests, but if your "chancre" doesn't heal for weeks, it is a good idea to show it to a doctor or test again.