Confused please help! First pregnancy!

So last week I found out I was pregnant and was estimated to be about 11weeks based on my menstrual. I had my first ultrasound today and they told me based on size I'm only about 4 weeks and 1 day. I saw the fluttering of the heart and the yolk sac as well. Then she tells me I may be at risk for miscarriage. What should I do? Should I get a second opinion or just wait until my follow up in 2 weeks? I've been very emotional of the thought of a miscarriage because I've gotten my hopes up for a baby. I'm really lost and confused. Any advice ladies?