It's certainly possible to increase by 150+ points from a week 3 practice test, so rest assured that you can get there. Practice test scores that early in the course are often held back by:
1) You're early enough in the program that you probably overthink questions that you would ordinarily get right quicker (you know there's a strategy but haven't really gotten comfortable with it through homework.
2) You haven't done much with pacing, so you're likely making rushed mistakes and/or not finishing sections completely.
3) It's hard to be entirely focused on a practice test while you're balancing work, class, homework, etc.
4) The practice test scoring algorithms are pretty good approximations of the official scoring system, but not exact (GMAC has its own proprietary scoring system), so typically the scores skew a few points lower than what an actual score would be (the theory is that, if they're not perfect, we might as well encourage people to study harder than to get complacent)
Given all of that, it's quite a bit more important that you learn from the practice tests you take during class than it is what the score shows. Go back and determine why you made the mistakes that you did - do you need to focus on those content areas? Do you make the same careless errors repetitively when you're under timed pressure? Did you simply not have enough time to finish the section?
Use the practice tests to help you determine where to spend your study time, and you can certainly make up a lot of ground.