Concur with the above suggestions to relax and enjoy yourself, staying safe above all.
Strongly suggest you practice drawing your pistol from under your jacket/shirt/vest at home and dry-firing.
Also suggest you practice the "tactical reload" or "reload with retention" - it's a pretty important skill in IDPA. For the match, consider wearing pants/shorts with nice, wide-mouthed front pockets or cargo pockets to throw your retained mags into.
Don't "crowd"(get too close to) your cover, and work on keeping your feet and torso behind cover as you lean out to engage targets - you'll be penalized if more than 50% of your torso is exposed from your cover. Learn to "slice the pie" - only move out from your cover just enough so you can see just the one target you're engaging, and NO OTHERS; if you can see multiple targets, they can "see" you and therefore can "shoot" you.
If you can, try to get in a little live-fire practice a day or two beforehand, just to work the bugs out. If your range allows drawing & firing from the holster, do that and concentrate on a well-aimed first shot from the holster. Also work on "double-taps" and "hammers," not to perfect your technique necessarily, but just to get yourself used to firing those two shots in rapid succession at your target.
If you come across targets farther than 10-15yds away in a stage, SLOW DOWN and SHOOT DELIBERATELY. It's better to take an extra split-second to GET THE HIT than to go fast, assume you hit the target, and eat an extra 2.5 seconds for missing it. Also, don't be afraid to fire an extra shot or two to make sure you DIDN'T MISS, as long as the stage doesn't limit the # of shots fired.
Finally, keep in mind that any schmuck can shoot poorly, fast. You need to concentrate on shooting and moving smoothly and efficiently - if you can do that, you will automatically shoot quickly, accurately and SAFELY. Don't obsess over winning the match, looking good, or even not embarrassing yourself - focus on each stage and the tasks required in each stage, and your efforts will be rewarded accordingly with your score.