It’s too late for
@aliciag56, but for others who are wondering about the three day window:
The CDC is very clear that the requirement is a test within three days and not 72 hours, which opens up more leeway for US-bound travelers.
The 3-day period is the 3 days before the flight’s departure. The Order uses a 3-day time frame instead of 72 hours to provide more flexibility to the air passenger and aircraft operator. By using a 3-day window, test acceptability does not depend on the time of the flight or the time of day that the test sample was taken.
For example, if you are fully vaccinated and your flight is at 1pm on a Friday, you could board with a negative test that was taken any time on the prior Tuesday or after.
And it is equally clear that a rapid antigen test is acceptable.
As is always the case with info given on this topic, all we can say with certainty that these are the requirements in force today! You should always make sure you have seen the most up to date information, and the US embassy websites are probably the best place to go.