First time mommy question

Macey • I'm 18yrs old second pregnancy first child a boy. Who should be arriving around December 4th 2015, his name is Patrick James Noonan and daddy and I are still together.
I just turned 18 two days ago, I am currently 30.1 weeks pregnant. I went to my girls can ultrasound about a week ago and his estimated weight is 3.4 pounds. I was wondering if I should be worried about this or that is too big of a size? I was also wondering if I should start thinking about being induced if he is too big ever since I'm so young or if age doesn't matter for size down there lol please give me advice if you've been in this situation or could help at all I'm really worried!!! I also used to weigh between 94-104 pre pregnancy and today I am weighing 148 and I don't exercise much at all to be honest.