Oh don't we all have these days.  You can see so clearly the picture of a scene in your mind.  It's a masterpiece.  You rush to write it down.  And out comes... mush.

You've seen the memes.

It happens to all of us.  Ahem, much more than we'd like to admit. 

It's an unfortunate reality, not everything that pours out of your magical fingers is going to be perfect.  But you know what I am going to say - practice makes perfect. 

The violinist doesn't get those perfect notes in that recording without hours and hours of practicing, going over and over the notes until they are...well...perfect.  

Keep going over your scene, rewrite, remove, start over, get feedback, ask for help, read someone else's scene. Make it perfect.