Write Away

I wouldn't worry about it too much if I were you. I outlined the novel I'm revising now pretty well and I still ended up with a completely new outline full of big changes for the second draft. I think it's easier to see what works and what doesn't and possible solutions when the actual story is in front of you. But I'm very much an exploratory sort of writer where the first draft is just a fun mess meant to get everything down on paper, so that may not work for you.