The poster did not come into the country on an adoption visa (IR-4), so there was no automatic citizenship. S/he will have to apply for a green card and eventually citizenship. S/he needs to prove that s/he has lived with the petitioners for a minimum of 2 years and that they have had legal custody for that time period. The clock starts once legal custody has been established, not at the point at which the adoption is finalized (which can be substantially later).
OP, you should ask your new parents about the date on which their petition to be your legal guardians was approved. It sounds to me like that would be your starting date, so you would be able to start your application for a green card two years from then. You may want to consider a gap year because the green card process will take a while and you’ll want legal residence for financial aid and other purposes.