Hi Kim,
Based on what you've described, there are a number of different 'issues' to contend with, so I'll deal with them in a logical order.
1) Your goal score is absolutely achievable, although it's not clear how exactly you know that you 'only need' a 400. Is that a minimal score requirement for a School/Program that you're interested in? And are you GUARANTEED to get in if you score 400+ (how do you know?)?
2) You can achieve that score goal without correctly answering ANY questions that you think are too hard or too weird, so don't worry about those prompts. However, you have to take a good look at the questions that you DO think that you can correctly answer - on the ones that you're getting wrong, can you explain WHY you got them wrong (those errors are the things that you need to focus on eliminating from your work).
3) Many Test Takers spend 3 months (or more) of consistent study time before they hit their 'peak' scores. Part of your issue is that you have not put in enough time and effort yet.
4) You've used a book-heavy approach so far during your studies. Many Test Takers get 'stuck' at a particular score level when studying in this way, so you might find it useful to work with some new, non-book study resources.
5) The two score results that you listed likely vary because you're guessing a lot in BOTH the Quant and Verbal sections. While you could conceivably 'guess' your way to a 400+, that really shouldn't be your chosen approach.
A couple of weeks might not be enough time for you to 'lock in' the proper skills needed to hit your score goal, so you might want to consider pushing back your Official Test Date a bit. What are the application deadlines for the Program(s) that you're considering?
GMAT assassins aren't born, they're made,
Rich