When you were pregnant, was your placenta on the bottom?

I'm only 15 weeks, but we had to do an ultrasound already because I have to have oral surgery and they wanted to make sure about how far along I am. The doctor told me that my placenta is on the bottom, and that I need to be careful because if it slips I could hemorrhage. But that's all they told me! Is there anything I can do to make it safer for myself and the baby? What's the technical term for it so that I can look it up? I'm freaking out and my doctor was in a hurry cause they had a delivery to get to. I could really use some help from women who have been there.