First of all you will be fine. You sound scared. I get the impression you feel your not ready to be a mammy. Give yourself time to think. Are you sure your family can not offer support, sometimes they can surprise you. You need to talk to somebody. Go to your Doctor
I assume you are saying that your boyfriend's mom saw the test and knows you are pregnant? What did she say about it, was she supportive or the opposite? If you are sure your family will not accept the situation, the next obvious place to go for help and support would be your boyfriend's family. Do you live with them? (I'm trying to figure out the scene in which your boyfriend's mother would be standing right there when you walked out of the bathroom. Was she visiting your apartment where you live with your boyfriend, or was this in her house?)
Your family's reaction will probably also hinge on how old you are and how prepared to take care of yourself in the world. If you are 25 with a college degree and a good job and good prospects, then your issues will just be logistical, such as finding good daycare and a way to pay for it. If you are 16 and haven't finished high school, your family will be worried about your survival. You'll need to tell them based on your understanding of what they are likely to worry about.
I was scared to tell my mom . I found out when I was 4 weeks I didn't tell her until I was 10 weeks. And when I told her she took it very well . I didn't know what to do either. My boyfriend signed me up for insurance and I started looking a doctor. I went to the doctor when I was 8 weeks. My boyfriend had my back 100%. I have a aunt that I can trust with everything and I talked to her. So maybe you might a mentor or a aunt that you can trust that will help you.
First, breathe. Don't freak out just yet until you have it confirmed by a doctor. In the meantime, you do have options that you can consider. Discuss your options with your boyfriend and decide what would be best for you two and your baby. Then go from there. If you need someone to talk to, talk to your doctor or find a pregnancy resource center in your area if you have any. They will be able to give you advice and they will know the right resources you need to have a successful pregnancy and/or be able to help you with the things you need should you plan on raising the baby. I'm not sure how to tell you to break it to your family, but maybe they'll surprise you and be more supportive than you think. I was in your shoes at one point. Pregnant and scared when I had my first. It will all work out somehow.