Over-trimming the jib in relation to the amount of trimming of the main results in pulling the bow to leeward. The boat finds its way to a lower track coming off the mark. In fact, on our boats the jib is completely luffing until we are on a close hauled course, then the crew snaps it in. This is popular with the crew, too, since it is so much easier to trim. Need the main trimmed more and the jib not so much yet.
Fouls are slow.
Accept losing a boat or two instead of committing a foul and turns or damage. That's another reason that anticipating and planning the mark rounding are important. You've got to figure out how you can accomplish a fast and clean rounding well before you get into the fray. Developing the skills and technique to be fast through the turns can be practiced with just one boat by itself. With practice, you'll be able to tell when you're making the turns better and leaving the mark at top speed.