Even if you did put your head underwater, it's still not a like infection:
Naegleria fowleri infections are rare*. In the 10 years from 2008 to 2017, 34 infections were reported in the U.S. Of those cases, 30 people were infected by recreational water, 3 people were infected after performing nasal irrigation using contaminated tap water, and 1 person was infected by contaminated tap water used on a backyard slip-n-slide.