Need to fly with my cat in a carrier under my seat. Can I be SURE that I'll be allowed to fly?

First off it doesn't go under your seat it goes under the seat infront of you.

If you've made the reservation for your cat the pilot can't refuse you or anyone for that matter. While it is true that they only allow a certain number of animals per flight in the cabin if you've made the reservation for your pet you're set.

Just make sure you go to the vet no less than 10 days before the flight and get a health certificate and make sure your carrier is small enough to fit under the seat. Airline websites all list the max dimensions of carriers. Just Google "Delta flying with pets".

BS - you paid for the ticket to fly the cat in cabin with you - don't worry you will be allowed on the plane with the cat. You don't have to worry. Flights only allow 2 animals on board on that particular flight. They would tell you ahead of time if you need to make changes.

I took my cat to a show and the stewardess asked me what seat I was in cause she was allergic. I have Ocicats that don't shed. Funny thing was the cat was quiet as a mouse and she later had that cart in the aisle and never once sneezed being near or next to the cat on the floor.....lol

You need to check at the time of flight or as you say very early day of, unfortunately you could be denied. That is rare so do everything they told you and it should be fine.

Call them to ask then ask a vet just in case to make that fellow sleep or to be calm in the plain