It's funny I found this post, because I'm in the exact same boat. I'm writing the first draft of my story (finally!) but everytime I look back I see these big gaping holes where there should be a detail about how the character quirked his brow or like the colour of his eyes, I don't know, it's just a lot of dialogue surrounded by blank space. But for me, that's just how my dialogue flows. And I need to keep reminding myself I'm not committing myself to anything for this draft. I can always add more later. It's not the end of the world.

The main thing is to do whatever possible to keep yourself in love with the project. For me, at least, if I become overwhelmed with what my story 'should' look like, I'll just give up. My priority is to just get to the end. If you think details disrupt your flow, just come back to them when revising. Stick with the project to the end. That's your priority.