soul_survivor,  like Churse said; legally you are an American citizen.   You must use your American passport whenever you travel and you will be safe.   The moment you use your Nepali passport; it will be 100 % illegal and you will be in trouble big time.   It is good to be smart but never try to be too smart by doing anything illegal.   Let's not forget our old saying:   "लाटो खान्छ एक बल ड्यांग, बाठो खान्छ तिन बल ड्यांग "  Thanks