I'd say don't worry about it now. First, backstory makes the characters and the actions they take. Therefore it is important. Then when you can, try to push it into conversations and other areas with one or two sentences at each time, rather than writing it in one big chunk. But if you've already written that big chunk, don't worry. Just go ahead. When all finished, you can fix it.

In my case, it will be unnecessary scenes or excess dialog in scenes that I'll have to get rid of, later. Right now, I'm just writing.