You're doing nothing wrong, you just haven't been at it long enough. Keep incorporating intervals and hills into your rides and you'll get faster, assuming you're putting in enough overall mileage. Set a minimum base of say, 150 per week, and try to get over 200 when you can.

But 30 mph on even a flat surface for any extended distance is way fast, unless you're riding in a pack.....are you certain of that velocity?