"over my head"

"maybe I'm a little bit over my head"
How could you be "over your head"?

It's an analogy to swimming. Young children, especially, are told not to
"go in (the water) over your head." Later in life it's used to describe a situation that you can't deal with effectively.

Agreed. The obvious phrase would be 'I'm in over my head'. Adding 'a little bit' has confused the writer as to where to put the 'in' so they've left it out all together knowing that readers will 'get the gist'.