If you have vaccinated them shortly after hatching, and before exposure to other birds, you probably are going to be ok. You may want to keep them seperated for a few weeks - I'm not sure how long it takes for immunity to build after the vaccination. You may want to check with the vaccine manufacturer on that (or google). I don't think a second vaccine would make a difference - I think immunity will build just fine on the .2cc dose.
I share your fear - I just innoculated my first batch of hatches two days ago and am worrying about everything from did I get it enough in and properly to what if they have a vaccine reaction. So far, they look great and I figure they need to brood for at least a couple more months before heading outside so I am going to trust that I did the best I could and that they will be fully immune by the time they feather out and go outside.
Good luck! Breathe...
