Re: I'll never stop "improving"!
From one 'skinny' to another, welcome to the forum. We're glad you've benefited from the information available here and advoided some of the problems that can be had with a first time build.
35mph isn't an unreasonable expectation. It is pushing the top for a stock engine and low gears. A 40 tooth sprocket, even a 36T if you don't have big hills, will help as well as proper carburetor tuning. You'll want to gap your plug to about .024 for starters and run a good fuel/oil mix, something in the 32:1 to 40:1 unless you go with one of the exotic/synthetic oils which require much less; 50 or even 100:1.
Watch your spark plug color and shoot for a nice brown. Explore some of the expansion chamber exhausts but you'll also have to re-tune the fuel/air mix using them. Also be aware that the Chinese 2 stroke engine perform better and better as they accrue miles. They're somewhat slow to break in and the more miles you put on them the better they'll perform.
That said, please concentrate on the bike before worring too much about speed. Brakes, bearings and frame integrity are critical.
Have fun and ride safe.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"