The only purpose of the take away is to establish an initial path, rhythm, and tempo for the racquet to get into an effective throwing position. Sampras sends the racquet head on a downward and then loops it back up. Krajicek takes it back horizontally, and then lifts it up into the power position. Ivanisevic draws the elbow at an almost 45 degree angle into the power position, which allows him to short cut the path. You definitely do the waiter's wrist thing on the way up, and many people see that as a flaw. The simplest solution is to make sure that the thumb and racquet head face the sky more, and also to avoid creating such an acute angle between the forearm and the upper arm early in the swing. I basically maintain a fairly flat wrist while keeping a 90 degree between my forearm and the upper arm the moment before I swing the racquet upwards. Most big servers decrease the angle as they make the move upwards, but you start the racquet out in that acute position and maintain it until you make your move up at the ball. A more classical takeaway and throwing motion would likely allow you to create more momentum into the upswing, which should translate into more effortless racquet head speed. If you have to compete by Sunday I probably would not make too many adjustments, it could just drive you nuts. If you are dedicated to building a great serve then get some videos of Sampras, Federer, Krajicek, Ivanisevic, Roddick, and Philippoussis. Then study their serves in slow motion and make notes of the common traits each of their serves have. It is much easier to grasp visually than it is to interpret a tip on this board. if you effectively implement the techniques of the six players I have suggested, then their is almost no excuse to have a less than ideal serve.
