Hi Steve,
What strikes me as odd is the prop; if I see it correctly it spins clockwise (seen from the rear), while most single prop boats have a counterclockwise spinning prop.
Reason for this is the motor; most brushed motors have a preferred direction in which they run faster than the other way, this is called timing.
Unless the manufacturer has a shipload of clockwise timed motors he needs to shift, my guess is that the motor will spin faster in the other direction.
The problem at hand is the odd size of the shaft, which makes finding a counterclockwise spinning prop very hard to impossible...
Also, the pitch seems to be small, which isn't a bad thing, it'll keep the motor from overheating, but the speeds won't be very high (as you've noticed).
Another thing is the hull; with strakes that have the wrong shape; maybe this works best for such a small hull, but my small boats most definitely have strakes that look 'normal', aka have vertical sides and run perpendicular to the waterline.
Regarding a bigger prop, as Mike already suggested, be careful, specially if the motor doesn't have watercooling, it may overheat very quick.
If you can alter the shaft by converting it to M4 thread, you'll have the entire M4 threaded props of the world at your disposal; most likely in the 2318.XX series you'll find a Ø 29 and 31 mm prop with a slightly higher pitch, which should result in more speed.
Having watched the video a couple of times, it looks as if parts have been speeded up, the actual speed is hard to see due to the erratic driving...
Regards, Jan.