Knowing where your swing should bottom is important because the bottom of the swing will determine your impact location and whether you hit the sweet spot of the clubface
Do not put pressure on yourself as you approach the final few holes and have a chance to break a personal milestone, take each hole on the course as a separate game and try to win that hole, then move on to the next one disregarding your previous scores
Coming up out of posture during the downswing is a common fault created by a lack of strength in the glutes (buttocks), try stretching and strengthening them by lying on the ground with your knees bent and lifting your hips and buttocks off the ground for ten seconds