Possibly your Native American is too distant. These tests only go back approximately 6 generations. K13 is not really proof though. This is my daughter's result on K13 and she doesn't have anyone in her ancestry that could be Native American.
https://i.imgur.com/4TZfmVC.jpg
She gets these results in her mixed mode.
6 98.9% Southwest_English + 1.1% Karitiana @ 1.85
7 98.7% Southwest_English + 1.3% North_Amerindian @ 1.85
8 98.8% Southwest_English + 1.2% Pima @ 1.86
9 98.8% Southwest_English + 1.2% Mayan @ 1.87
14 98.7% Southwest_English + 1.3% East_Greenlander @ 2
15 98.7% Southwest_English + 1.3% West_Greenlander @ 2.06
Do you have other commercial dna tests that give you Native American like Ancestry for example? I would take more seriously results like that. If you have Grandparents still around it would be worthwhile getting them tested as they would be closer to the source.