Im ever so slightly red-green colour blind, is it possibly for my colour blindness to get worse over time?
Yes, but extremely unlikely.
Red-green colorblindness caused by your genes (which is what I’m presuming you have) will not change in your lifetime, but other things can change color vision in either the colorblind or in those with normal color vision
Some people are colorblind because of damage to the part of the brain that processes color, but I think this is so rare that it is practically never mentioned in discussions of colorblindness. One of Oliver Sach’s books describes a man whose color processing region failed overnight - a stroke or something. He awoke to find the entire world in grayscale, a very remarkable and somewhat depressing development. He would describe his view of the world as suddenly “leaden”. Anybody whose colorblindness is of this very unusual type could find it gets better or worse if that part of the brain is partially malfunctioning for some changing reason.
I imagine that if there were something causing damage to the cones along the back of your eyeball, it could compromise your color vision.
However, genetic color-blindness is an absolute. It is, or it isn’t. Any change to your color vision would be caused by something else.