Sydney Sweeney's taking one last lap around the ring ... sharing a ton of pics from behind the scenes of "Christy" and thanking everyone involved.
The actress dropped the pics the day after the film's wide-release in theaters ... with one featuring standing in the ring toe to toe with the film's namesake, Christy Martin.
The two are wearing complimentary outfits -- Christy does love her pink, after all -- and, they're grinning ear-to-ear.