How have you aligned your scanlines in the image setup panel? I.e. have you used 'Start', 'End', 'Centre', or 'Justified' in the option below Cache and above Map Style in the top left?
The reason that the image looks a little unaligned is that each scan line is slightly different in length (presumably because you're creating selections from channel values) and that they are not aligned.
My advice would be to nail down the start of each scan line with multiple criteria (e.g. Cu_ppm > x, Zn > y etc etc). Then, with nice and sharp starts to each scanline, I would align them to using the 'Start' option.
You'll notice above that the criteria I've suggested are the ppm channels. Remember that you can calculate ppm values without any sample selections at all, and then go back and select your samples. The advantage of using ppm channels is that they have been corrected for baselines and sensitivity drift. At a pinch you can try the baseline-subtracted
_CPS channels; they will at least have baselines subtracted). This should give you a more precise threshold for setting the start of each selection (the end is not as important because you're not aligning your scanlines using their end, and any additional data selected will just appear on the right side of your image, if you're scanning left to right).
Please let me know if any of that doesn't make sense, or improve your images.