The cassette has 8 cogs, with the smallest cog having 11 teeth and the largest cog having 30 teeth. The cranks usually have the size stamped on the back side of the cranks.

I have to agree with the above statement. I doubt you are pedaling fast enough, your cadence isn't high enough. Though it is not impossible for someone new to be going 35 mph, it is unlikely unless you are going down a steep hill. What is your cadence? Cadence is the rpm's of the cranks. People are different, but the most efficient is usually around 90-100. I actually like to spin a little faster, around 110-120.

Do you have a computer on your bike? How fast does it say you are going?