Personally, unless you have a compelling medical reason to deliver early, I wouldn't. I was induced at 40 weeks (medical reason) and my baby ended up in the NICU for breathing difficulties. We were told that the reason was basically that she "wasn't ready for the world just yet," like she was supposed to stay in there another week or two. Just because a baby is technically full term doesn't mean the baby is ready to be born. I don't say that to scare you, just to give you a reason to wait if you can. Obviously, if you have a medical reason -- complete previa, pre-eclampsia, etc. -- it's definitely best to go ahead and do it now. I just think it's best to wait until the baby comes on its own or at least closer to your due date (btw, the average first time mom who gives birth without being induced or having an early c-section delivers at 41 weeks 1 day!).
That being said, I'm sure your 38.5 weeker will be fine if you have the section now (my baby was! It just took a couple of more days of monitoring than normal to get her adjusted).
Ultrasound weight measurements are notoriously inaccurate. Your baby may be 6 lbs now (average gain of about 1/2 lb a week would make him/her about 6 lbs now) or 4 lbs or 8 lbs; I believe they're usually accurate within 2 lbs, which is a huge margin of error! I wouldn't worry too much about that.