Very Little Change After Botox on Forehead

If you have had forehead lines for a while, it will take a while to soften them up. Of course, Botox is designed to treat the underlying muscles that cause the wrinkles, but it does not actually change the skin. So, after the muscles are paralyzed, and done so on a continuous basis (meaning you have to keep up with re-treatments), eventually the wrinkles should soften up.
Sun damage, smoking, etc. can damage the skin and work to increase wrinkling. Protecting the skin, exfoliation and hydration will help treat the skin while the Botox works on the muscles that contract and can accentuate the folds (wrinkles) that are more likely to appear in damaged, as opposed to healthy skin.
Also, people require different doses of Botox. Some people need minimal units injected. Others need more. It sometimes takes a session or two or your doctor to figure out what dose works best in your case.

Annie,
It may take a few treatments of Botox to eventually smooth your forehead.  Look in the mirror and try to raise your eyebrows.  If you are unable to raise them, then your Botox is working.  Patience.