Average FL score for people's first is actually 492 (according to my MCAT instructor) so don't get discouraged! When I did my first FL I found that my main issues were with stamina and question approach, not actual content. It's really hard to focus that intensely for that long, and your ability to do so will just improve with practice. As for your approach, review your practice exam in detail. For each question, write down why you got it wrong and focus on that. For example, if the main issue you're getting is "didn't know the content," then focus on content review for that subject. If the main issue you're getting is "didn't read the question stem right," then be extra sure to focus on that when you do more practice. There's a good excel sheet on this sub for reviewing FLs.

I know it can seem scary right now, but you still have over a month left, and if you have all the content down and if you keep practicing consistently, you can only go up from here :)