OP, your dyno looks very rocky for a smoothing factor of 5 on the plot. If you have Winpep, load the data with a smoothing of zero, and you'll see it looking extremely jagged. Such a rocky dyno plot on smoothing of 5 is common on tuned N54s, but not M3s, so that indicates it more than just operator and/or environment. The car is not running right imho.
I would do a full PM on the car including changing the spark plugs (with proper gap), update the DME if at all possible. Then, drive it for a couple of days HARD, with several trips to redline in at least 3rd gear if you can do that safety somewhere.
Then, immediately dyno the car and enjoy 340+ rwhp. Whatever you do, don't dyno your car after you've been featherfooting it for weeks on end. You want to really wring it out under as much load (as high a gear as possible) as you can all the way to redline several times (to set your trims), and then dyno as soon as practical after that. If you don't hit that 340+ rwhp, do a compression/leakdown test and let us know the results.