Figure out which HP rating you have. If you have a 1hp model, that's probably about right. If you have a 1.5 or 2hp model, then something is probably off. Or well, no matter which one you have, you shouldn't have to dick with the throttle to get it to go faster -- that's probably a maintenance thing rather than what it's supposed to do.
A basic tuneup is always a good place to start. Clean the carb. Get an in-line fuel filter. Check/replace the spark plug. Clean the points. Check for spark. Check for air leaks once you've got the bike put back together. Make sure your chain is properly lubed and tensioned. Drain the transmission fluid and put new stuff in. If none of that helps, there are probably some other things you can look at, but this is all stuff that really ought to be done when you get a new moped. There's a decent chance you'll improve the situation with just the basics, and if not, then at least you can scratch all this stuff off the list of potential reasons why it's doing what it's doing.