My first suggestion to you would be to contact your nearest planned parenthood and discuss your options with them, so that you can make an informed decision if you are indeed pregnant.

When you say your family would "kill" both of you, are you being literal about that? If so, you should contact child protection because it sounds like you have abusive parents. I understand your fear of disappointing them but unless you fear actual violence toward you from them, please consider talking to one or both of them about this. If you are pregnant and decide to keep it they will find out sooner or later as your body changes.

If you know any adults you can trust to talk to about this, you should consider going to them...if only so that someone you know and trust who has life experience can advise you. Advice over the internet is all well and good but it can't beat talking to someone you know personally.

I'd also pick up another home pregnancy test or two and check again. False positives happen and stress can throw your cycle off.

I wish you the best of luck and I hope it's just a false alarm. Abortion is and unpleasant experience for anyone and childbearing/raising at your age could very well cripple your future if you don't have the resources and iron will to keep it from holding you down. I'll be keeping my fingers crossed for you.