It's difficult to tell from your pic what the issue is. Maybe a more detailed shot of the problem area? A carpet store might have some sort of welting or joiner strip in gray or a complimentary color that you could use at the seam.
"For every complex problem there is an answer that is clear, simple, and wrong." (Henry Louis Mencken)
2005 X2, Viper Red, MCX, Acme 1285, PPass, rear 750 sacs, KGB, IBS, Bennett Wake Plate
(previous) 2001 X5, 1991 TriStar 190