3 Week Old Baby Keeps Leaving Nest

As title states, I have a 21 day old budgie that keeps leaving its nest. It'll jump out and go for an adventure.

It's the only baby and parents are still caring for it.

I've lowered the nest and keep putting it back in when I notice it. I also have baby bird mix ready to go for just incase.

From what I've read this isn't normal and it's too young to be leaving the nest?

What can I do? Also when should I remove mum