Hi there!
I was doing my MRes and getting stressed out about achieving as well as possible, and my supervisors told me to chill out as once I had my PhD no one would care much for my MRes anyway. They said that people will want to know that I have a PhD, who my supervisors were, if I am published and how many revisions I had to do to be accepted as a PhD. SO I chilled out, got a merit and worked on my PhD at the same time! Try your hardest, obviously, but don't stress cause it won't be worth it.