Mobile internet is never going to be as good as landline broadband and is intended to be used when there is no other way of connecting to the internet whilst you are out and about.
If you get a very strong signal the speed should be better than dial up but not as good as fast broadband. If there is no signal you get no service.
Did you buy it over the internet or phone? If so, you can cancel and return.
"As the 3 service was PAYG, we did not cancel it. For other providers, we cancelled in line with their returns policy that allowed a full equipment and service refund. For Orange and T-Mobile, this was the minimum seven days required by the Distance Selling Regulations. Other providers offered a longer cancellation period.
Mobile broadband cancellation was straightforward with Orange � it sent a jiffy bag to return the mobile broadband dongle and didn�t take any monthly payments. We had to spend the best part of two hours on the phone to O2 over seven days, and spoke to six different people before being able to cancel and get details of how to return the mobile broadband dongle. O2 refunded the price fairly promptly once the dongle was returned."
http://www.which.co.uk/reviews/mobile-broadban d/page/mobile-broadband-put-to-the-test/