what is grounding your stake mount? If it is just touching paint, you have no ground to the vehicle and the coax is acting as counterpoise. A fire-stick is a terrible antenna. If you want great, look at a Larsen NMO-27 and be prepared to drill a hole in your roof.
Here's the plot for my Larsen NMO-27 mounted on the roof of a full size pickup:
Nice and even across the band. Center of the cab, permanent NMO mount.
Marker 1 is CB Channel 1. Marker 2 is CB Channel 19. Marker 3 is CB channel 40. The entire span of the trace is 26MHz to 28MHz.
Here's a close up:
This shows -just- the CB band. Marker 1 on the far left of the screen is Channel 1. Marker 2 is Channel 19, center of the band. Marker 3 is Channel 40, on the far right side.
I suspect if you put your antenna on an analyzer, you'd see your lowest dip would be somewhere above channel 20. I think your antenna might be a tad bit short.
But with your antenna mounted off to one side of the vehicle, it's going to suffer from a messed up ground plane. I understand that mounting them dead center of the vehicle roof isn't always an option, but it certainly has some benefits.
Depending on how much you are willing to tolerate to get your CB to work well, you may want to consider taking the next step, and putting a proper antenna on a good ground plane. It really does make a difference.
Unfortunately the people selling the gear want you to think it's all easy, bolt on stuff and it'll work fine. That's resulted in hobbyists missing out on a lot. Compromise antennas might be easier to install, but they don't always work well. If folks would understand how important antenna system are, they'd have a lot more luck with their radios.