Dust inside my lens, does that affect image quality?

Basically, the answer is no. Unfortunatelydust inside lens ispretty normal. Only certain expensive L series lenses are sealed to prevent air from entering. All others have a lot of cracks and openings where air - and dust - can easily enter. Zoom lenses which extend in length when you alter the focal length are particularly vulnerable to this problem, since air gets sucked in every time you move the lens barrel.
Luckily a little bit of dust inside a lens isn't going to make much difference, so don't worry about it. It may be alarming to see the dust specks when you hold the lens up to a bright light, but it'll cost an awful lot of money to have a camera repairperson dismantle the lens and clean each internal element. And there's no guarantee that the elements will be properly aligned when he or she gives it back to you. So unless the lens is coated with a dusty grey film of dust you shouldn't have any problems.