When I read your post- sorry, but I laughed a little- DEFINITELY NOT because I find your situation amusing; quite the opposite! I very vividly recall having those fears myself. I didn't pop my cherry till I was 18, because I was convinced that I would become pregnant the first time- even with protection! While all my mates were experiementing & loosing their virginity, I was petrified of sex because sex equalled a baby.
My fears stemmed from a few areas: my mother drumming it in to my head that she didn't want to be a grandmother; a fear of carrying a life inside of me; a fear of growing up & having to be responsable for someone other than myself- and most of all, the fear of giving birth. I couldn't quite figure out how a huge baby was meant to get out that small hole! I knew it stretched, etc- but the thought of it had me considering a nunnery.
I too did the doubling up- until one particular boyfriend didn't 'cover-up'. I fell pregnant at age 24, while on the pill.
And it was the best thing that ever happened to me. I wouldn't change what happened for the universe- my now 12 year old IS my universe.
Where does your fear actually stem from? Are you scared you would be a single parent? Are you scared you will disappoint your parents if you fall pregnant accidently? You mention your parents at the end of your post, but I didn't understand it in relation to your fear. Sex talk with parents is never easy! lol And you're 19 years old- why do you need to bring it up with them? Is it any of their business, unless you actually fall pregnant?
You are being sensible; trust yourself & trust medical science! If it did happen, then you would always have choices.
Best of luck & I hope you start to feel better & more relaxed about sex. Relationships & sex should be fun- not full of worrying about things that might not happen!