He gets stuck high in the air because he floats downward at an incredibly slow pace.
Unlike his earlier struggles to summon his shield, Steven demonstrates introspection by figuring out how to manipulate this new ability on his own. [S3E6] Steven Floats
I can provide whatever or lore analysis you need next! He gets stuck high in the air because
He wants a fresh, warm pastry from the Big Donut right when it opens at 7:00 AM. [S3E6] Steven Floats
Overjoyed to be back home, Steven leaps into the air and accidentally jumps hundreds of feet high.