Go to the Carnival website and click on the Have Fun, Be Safe link. Under FAQ's, about half way down the page, you will see a section about self tests. It has links that you can order your test to be mailed to your house. (Do not open the test until you are told to.) It's really easy, no appointment necessary. Sit down in front of the computer when you are ready to do your test, log in, a proctor comes up, verifies you (need ID) and your test. Walks you through the test. Leave it on your desk for 15 minutes and go about whatever else you need to do. Come back when the time is up, the proctor logs back in, verifies the result and emails it to you. All done!
If you have not used it, I highly recommend the Verifly app. You upload vaccination and test results while you are at home. A green box shows up around your picture once you are good to go and then you will spend less than a minute at the station that verifies your test/vaccination status. (I do recommend paper backups just in case the app is having issues.)
The testing is an extra step, but it can be done fairly easily with the right tools.