Many women have early ultrasounds done to check dating as well as growth of the child. I wouldn't worry much about it, especially if they didn't say anything.
Yes the is common and no nothing is wrong with you. Its just an extra precaution to ensure baby and you are well taken care of. at my first high risk app they did ultra sound and talked to doctor about possible risk with, my disease and ensure that I will be extra monitored so things go great. Congrats good luck and if you need to talk to anyone about having high risk pregnancy you can talk to me.:-)