If Botox creates too much of an arched brow it can definitely be corrected in order to lower the eyebrows. When discussing costs for a touch up, it really depends on the practice. Typically when you are charged per unit, a touch up, if needed is considered your responsibility to pay. In my office we charge by area and touch ups are free. I see my patients for follow up 2 weeks following their injection and I touch up the areas if needed. I would suggest you contact your doctor's office and find out if they charge for touch ups.
This is known as the Mephisto look and occurs because injections were not done laterally enough so return to your doctor and it is easily corrected with injections into the lateral forehead area