Improvisation, in music, rarely means “making it up.” Yes, we decide which notes go where, and are likely creating something never heard before.
But we’re not making up new notes. We’re not playing them in a new order. If you play “the blues” then they usually go in a certain order. If you play “jazz” then they go in a different order. If the notes don’t go in any particular order, then that’s a kind of order too.
But improvisation is spontaneous and risky all the same. If we’re not “really” making it up, then what are we doing?
Improvisation is the music of right now. It’s not the music you practiced, it’s what you’re playing in the moment, composing on the spot. Making it up is a nice idea, but what can you do to connect to right now with your improvisation?