Mirroring a sketch

So I’m trying to design a cage for a truck i’m building, i have a 3d scan of the truck in cad, and having issues mirroring my sketch for the a pillar bar, though i did the same thing with the main hoop and didn’t have any issues, I’ll try to explain as best as possible.

I started by making a datum plane on the floor of the truck mesh, and drew 2 construction circles where I wanted the bars for the main hoop to contact the floor, drew a construction line connecting to each point, and then used the midpoint constraint and drew another line up at a slight forward angle to represent where i want the middle of the hoop and the angle in reference to the roof. I then sketched half the hoop and mirrored the other side. The mirrored sketch didn’t line up with the other point on the floor so i just used coincidence to match it to the point on the floor and to the midpoint of the main hoop and it worked.

For the a pillar bar though, i can’t even mirror the bar. I started a separate sketch from the main hoop so id be able to label the different bars. I drew 2 more points in the footwell on the same floor plane I made earlier, and sketched the a pillar bar from the main hoop to the point in the footwell. I also drew a construction line from the point in the footwell to the back point for the main hoop(on the floor plane). When i try to mirror it, it won’t let me select the sketch to mirror. If i select the sketch in the browser and then hit mirror, it shows it as selected, and i can choose a reference point, though it doesn’t line up at all when it mirrors. When i try to constrain it to the points i want it to connect to(main hoop and floor) it warps the sketch, and if I try to constrain the sketch further so it doesn’t warp, it won’t let me align the 2 points anymore saying it’s over constrained.

What should i do to get it to mirror the sketch and align to the points I’ve drawn on the floor, and not warp ? Also, why are the sketches off from my other points when i try mirroring it on the centerline of the 4 points i made on the floor ? Why is it not symmetrical?

I’ve made a construction square from all 4 points on the floor and drawn a centerline down the middle of the floor from both midpoints assuming this would help it be perfectly symmetrical by choosing the middle line as the mirror line. Please help , let me know if you guys need more info or pictures. Side note, I tried to just sweep the first a pillar bar sketch with the pipe tool and mirror the body instead of the sketch, but doing that i can’t select the midpoint of the bend on the pipe without the sketch, which prevents me from making the windscreen bar. I also couldn’t align the body to the points on the main hoop and floor i want it to align to.

Some pictures or even uploading your model file would help a lot. It's always hard to try imagine these things.

I'm not 100% on your misalignment issues.

I'd say the mirroring issues comes down to using 3D sketches. From what I've found you can only mirror a sketch on the active or initial sketch plane, which is why your main hoop would have worked.

When you have a 3D sketch off the initial plane you selected for the sketch - like for one that follows the A pillar - it won't let you select the lines for the mirror tool.

I'd assume you want the A pillar bars to be direct mirror image of each other, and most likely the majority of the cage will be symmetric.

I would sketch half the cage, use the Pipe tool, to create the solid bodies, create the notches etc and then mirror the solid bodies.