if you really have "mediocre preparation and scores" i'd recommend you not to apply for residency in the States because the chances of getting into one of the programs are rare.
and it's really hard, you need a lot of preparation, do really well in USMILE, have good MBBS scores, good letters of recommendation, etc. it's all because of competition. you'll be competing with other MD students in the States and residency programs want the best candidates.
so, based on what you said, i wouldn't recommend applying for residency here in the States. but if you have money to apply, take USMILE, and time to prepare for it, try your luck. if not, specialize on something in Nepal, after all doctors get paid really well there too.