When I look at the pictures of Gambit that you posted, two things stand out to me when it comes to first impression. His hair and, in a sense, his eyebrows.
Your hair a lot shorter than his in the pictures, and your eyebrows are lighter in colour and not as dramatically shaped. The latter could be hard to do something about, of course, unless you use makeup to enhance them (which I think might look awesome, and also give you that badarse look Gambit has).
Actually, the kind of fringe you have in your forum avatar picture looks more like Gambit's. But if that is not an alternative I'd suggest getting a wig. Nothing can ruin a costume so much as the wrong hair, since even if it's not very noticeable, something will look odd and out of place. At least it would to me, but I admit that maybe I'm just a sucker for details like that.
"'Twas brillig, and the slithy toves
Did gyre and gimble in the wabe:
All mimsy were the borogoves,
And the mome raths outgrabe."