Write it out until you figure it out.
I put this sentence in an email once and was quite entranced with it after I wrote it. It's true. You have a scene in your head, and you want to get it on paper. Keep after it. Write and rewrite until what you see in your head ends up on the page. You'll know it's right if you keep going back to read it again and again because it feels good. I know that sounds hokey, but it's true.
In My Mother Grows Wallflowers, there’s a scene at the river where Sam and Mina share a first kiss. It was more than the motion of putting words to paper. It was the feeling the kiss evoked deep in my gut that needed to get on the page. The kiss, their foreheads touching, the wonder, and the deliciousness of his smell...all of it. I wrote and rewrote until it played out on the page the way I saw it in my head. To this day, when I go back and read the scene, I still feel the "Ahhh..." and wonder of that first kiss.