Am I a already a citizen?

[MireyaF]

I was born in Honduras in 1977, came to the United States and was adopted by a US Citizen. I originally had an alien card, but after my adoption I no longer used the card, my mother assumed I was now a US citizen. I recently requested my birth certificate from Utah, (the state where my adoption took place) they were unable to find it, once I gave them all the missing information, (my adoption records) they issued a delayed Utah state birth certificate. I have that birth certificate now. I have assumed all this time that I was a US Citizen, now I have been told that might not be the case. I need information on how I find out if I am a US citizen and if not, how do I become one, what forms do I need? Also, if I go for a passport, will the agency accept a delayed Utah birth certificate? (Just FYI...the birth certificate shows Honduras as the place of birth, but it also shows my US mother/adopted mother as if she was my actual birth mother.)