Don't worry simply. I doubt MN will delete (they don't often delete a baptism of fire :)) but every single poster has been flamed for something or other at some time. It's a rite of passage in a way, and everyone will have forgotten about it in a week. Sorry I did not realise you were new (or that your baby was quite so new! Congrats :) ) or I would probably have been a bit more balanced in my post.
Stick around, it is good here, honest. Go on active to see what takes your fancy, avoid AIBU, look around, yes definitely do more reading than posting at first and stick to safe topics, but before long you'll find yourself posting opinionated stuff without a care in the world - MN is great like that, people can handle a strong opinion, they might disagree but they won't hold a grudge.