everyone makes a mistake once on a while -and this isnt a bad one either- its just a little bump in the road, and you both should get it out in the open with your families, now while its still really early in the pregnancy, so your families can have more time to accept this little life that is coming into the world.
The earlier the better. You both may be scared of telling them, but your both adults, and you both are acting in an adult manor having unprotected sex, so do the adult thing, and tell his parents.
Get your plan worked out, like finances, living arrangements, health care costs etc.etc.etc. because they are definately going to ask you about these things, so make sure you can answer them right when their asked instead of saying i dont know. They may be angry, upset, disappointed...but dont argue with them when they say something, just listen openly, be calm, and answer what they ask you guys. Talk to your boyfriend about the sooner its in the open, the better.
Then when you've told his parents, maybe you could go with his mom or a close friend to tell your parents, because they deserve to know as well.
But the sooner you do this, you'll be able to make doctors appts. which are important, not have to hide such a big thing from everyone, you'll find out when your due date is too.
you were old enough to have unprotected sex, so your old enough to be responsible for your actions now.
good luck