gearing is a big issue, you only have one so dialing it to where you need it is important.
my bike is heavy, and I have a lot of hills so my bike is slow. That's that.
also if the engine isn't broken all the way in yet almost half of your potential power could be missing. my two stroke was super disappointing to me until the day I was riding it and it made a sputtering noise slightly like two stroking for a few minutes, I seemed to be getting more power during the sputtering, so I tried giving her some gas to see what would happen. this was the moment the engine completed it's break in cycle, the "sputtering" was the engine occasionally getting good compression and ignition. banging the gas seated the piston rings properly, combined with the warmed cylinder and few months of letting it wear in beforehand, I immediately got about twenty percent more power across the RPM band.
but if you live somewhere flat you can always swap out the rear wheel sprocket with a smaller diameter one.
think about driving a manual car, if you leave it in first the car takes of great and tops out at about ten KPH.
if you try and start from stopped with the car in fourth gear you may not even be able to make it take off, but you will maintain whatever terrible acceleration you have until the cars top speed.