- Should copers pour, connected to gnd, be placed around that signal ?
I do not do that. However, I often use 33R series termination resistor. As @qdrives pointed out, I just posted a video which could be useful for you:
https://youtu.be/CDJn-35W8sgAbout the distortion - it looks to me, like the output is weak (what are your output clock pin settings - e.g. push/pull, open drain, weak / slow, strong / fast, etc ...) or there may be a big load on that track (?)