17 and pregnant

im 17 and i havent had my period since march. took two pregnancy tests yesterday and theyre positive, as well as im having tons of symptoms so its pretty obvious. 
my fiance and i (yes were engaged) want to keep it. i didnt want to at first but after doing alot serious thinking, i want to keep it.
im terrified to tell my parents. I was already scared to tell them originally, and now that i also want to keep it im even more terrified. Im so afraid theyre going to disagree with me. i dont live with them and havent for over a year but i dont want to do anything to tarnish our relationship. although my mom also accidentally got pregnant at 18 and thats where my older brother came from, im afraid they will get mad at me for not learning from
that. 
any advice or suggestions of how i should tell them would be nice... no negativity please i really dont have enough energy for it im already stressed enough