If you want to show that you got married in Nepal and want to register that marriage then you need to have the certificates from nepal itself and you don't have to register to any offices. You just have to show the certified copy to the agencies when they ask for one such as changing F1 visa to Depedent(F2) visa. But if you want register marriage the easiest task is to go to the county court house (boy and girl) and obtain a marriage licence for a fee fo $ 30-50 and then get the authorized marriage celbrant to perform the wedding, it can be done in a day. Only difference will be tthe wedding date. Date will be the day the marriage celebrant signs your paper. You can get the cerfied copy later on from the county court house. Hope it will solve your dilema.