I hate to say it, but if that is at 4 months old, it is a female. By 4 months they should be showing a good deal of color. As a comparison, here is a picture of my 3.5 month panther. You can see all of the greens and blues, with some yellow and red peeking through. The peach color of your panther screams female.
If that was sold to you as a male, and you absolutely don't want a female, then I would contact the breeder you got it from and see if they will exchange it for the ale you thought you were getting. Otherwise, you have a beautiful, healthy female.
That is a female, the base of the tail there would be a slight bulge if not it would be thicker. The colorings of the chameleon also indicate female colorations.
Maybe you can contact the breeder and talk to them, maybe they will be willing to switch her out for a proven male.
Edit: Either way, she looks like she is in a great home and looks very healthy. She'll be a beautiful female. Sometimes they are underrated in my eyes due to the fact they don't show the vivid colors that a male may show.