That'll happen from time to time, don't worry.
Chances are, you may be on a shared connection with your area, and so, if a lot of people use it, you won't get the full connection.
Check at night, like after 8pm, and in the morning, and you'd probably get the full amount, as a lot of people tend to be on the Internet in the afternoon.
How far away are you from an exchange box? The closer you are to that, the more of the connection you'll get.
Also, is there anywhere closer than 100 miles? That ping is high for an Internet test. My pings from where I am are around 14-19, using the servers closest to me.