You will do FINE!!!!! If I can get through a move across the world, lol, you can get through this!! Just keep your lists in check and BREATHE and relax. You still have so much time!!! Yes, make sure your carseat is aircraft approved! They didn't check mine in the states, but when we had to change airports in Tokyo, they made this huge deal about checking it to make sure it was approved!!! I know that all Britax seats are approved, and my evenflo triumph is also approved. Read the stickers on your seat, it's proly there somewhere.
BREATHE!!
And don't bother bringing too many snacks and toys on the plane b/c you proly won't need half as many as you are thinking!!!
And yes, try not to stress about forgetting something...you can always buy what you need when you get there!!