Like most medication, the neurotoxins like Botox, Xeomin and Dysport are dose dependent and wrinkles/creases are not all black and white. The amount of Botox suggested may vary depending on your areas of concern, how much muscle activity is seen, and the muscle mass (e.g. men generally need a higher dose because the muscles are thicker). Generally I have my patients point out the areas that bother them and have them scowl, squint, frown, raise their brows in a mirror and then I point out the which muscles we want to weaken or paralyze to obtain the desired outcome. If your forehead has "deep" wrinkles or go all the way across, this would indicate that more botox might be needed. If you animate or create the "11" creases during normal conversation, I might point that out to you as well. 20 units is generally enough for the glabella and lateral brows for most women. 30-40 units is usually enough to treat glabella, lateral eyebrows and forehead.
If too little is used, the patient will not have the desired outcome and may be disappointed or think that the botox didn't work; in these cases the botox is working just fine but just not enough was given (it would be like taking a baby aspirin for a whopping Migraine).
My advice is to see how you do in the next couple weeks. Because it's not an exact science, sometimes figuring out the proper dose for the individual is a learning experience for both patient and doctor. Hope that helps.