I know this all too well.It could be a matter of perfectionism, and you just need to take it slow and edit as many times as you need until you can feel it's good enough. Because you can picture it so clearly in your head, you want to make it justice on paper and that puts a lot of pressure on you. And that perfectionism is paralyzing/blocking you, thus making it come across as clunky and not at all what you wanted, or how you wanted it to be.
My suggestion would be to move on to other scenes and not force it. With any luck, when you come back to it, the pressure will have lessened / disappeared, and you'll be able to try again even if it takes you longer or a few more tries than you thought it should.
That's one option. Another one is that, even though you want that scene, you like that scene and you can "see" that scene, maybe that scene isn't right (or the right one for this), and your subconscious is trying to tell you to find the right one by not letting you write this one. Ask yourself; if not like this, then how? How else could I go about this thing that needs to happen? Or, should it even happen like this at all? Should it be changed entirely, and/or maybe let something else take its place?
Sometimes, when this kind of block happens, it's just our brains trying to tell us there's a better way to do things, and to keep trying until we figure it out.
