I recently had Covid and you can test too early with an at home test. On the day I felt very sick and ran a fever, I tested negative. I was pretty sure I had it as my husband had tested positive four days earlier. Next day I tested and only a faint, barely visible line for positive. Day two, a full blown dark positive line. So that is what the above poster meant about the test being "more positive". It has to do with viral load. Antigen tests are not as sensitive as PCR tests. PCR will pick up any trace amount of viral load and show positive. You can have fever and symptoms and it still take two days for an at home test to show a strong positive. Frustrating.
As for the comment about the mask, even when you've had the virus for 5 days after testing positive and are fever free for 24 hours and considered no longer contagious, it is still recommended you mask when in public for an additional 5 days (total of 10 days from onset) on the slight chance that you might still have a low amount of viral load that could infect someone.
Hope this helps.
gpnfish, take care and I hope you are well and feeling better soon. I know it's disappointing to come down with the virus right before your cruise. Hopefully, if not this sailing, you will be sailing soon.