The lack of compression should be looked into. If it's still in warranty and you desire too, send it back for repairs. Any engine with rings should have good compression from the start. If you are out of warranty and want to find where the compression is missing. Take it appart and inspect the rings and cylinder walls for problems. There are people here in the states who specialise in ring replacement. ie.Bowman rings. If your engine has the same horribly inadequite machine work I've seen in other china made engines, a lot of bench running might be needed to grind things into shape.
Kinda tough for a ring to seat itself with blowby leaking hot gasses and carbon grit past it.
Otherwise your rpm's sound about right for a whimpy (no compression) 50cc.
Then take into consideration a wrap around pitts type muffler is about the most power robbing type there is.