You will be fine. I'm sure that the tech had collimated to the neck area of your son. And you wore the led. The collimation, is when they only radiate the area of interest. This was just the neck so that "lihgt" was only around the neck of your son. It also acts as a sort of radiation protection because it's made out of lead too. So you were "double" protected. you will be fine. Good luck.
I am pretty sure your okay. A lot of women get x-rays at the dentist, etc while preggos. Your exposure was most likely minimal. I think the only time you should worry is if you get multiple x-rays everyday, which is unlikely anyway.