I'm planning to travel to the USA and I feel concerned about the false positive rate of antigen tests for Covid-19. Unfortunately, there aren't many places that offer PCR tests with quick enough results to work with the current 24 hour test window mandated by the USA. So, say I get an antigen Covid-19 test and it comes out positive despite that I have no symptoms, and then I get another (either antigen or PCR) that comes out negative, can I use the negative one at the airport to prove that I'm not infected, or am I "tainted" and unable to travel there until some time has passed?