air travel – Different airlines, same destination, same day—can I check in at both?

OK so I booked with JetBlue then saw that their historical performance for this flight is horrendous ( I then booked another flight an hour later with American Airlines. I thought, why not attempt to check in with JetBlue first and use American as a plan B?

Ie if there’s a huge JetBlue check-in line, then go with American, etc.

Will this cause any issues at the airport with security? For what it’s worth, it’s the Cancun airport which is pretty disorganized.

Also—if I check in with American and go through security, but then my some miracle the JetBlue flight is on time, can I just show up at the gate and check in then and there?

Don’t want to violate any contract of carriage rules, etc.