So I did something incredibly foolish and created a sequence with hours worth of work at the wrong resolution.
I've been searching for answers everywhere and the suggestion of creating a new sequence (at the correct resolution) and copy and pasting the clips from the existing sequence to the new one.
It has sort of worked - In that three or so clips have gone back to the full resolution 2.7k but some haven't.
I have checked the properties of both of the clips and they are exactly the same except the 'Fit to Frame' has no effect whatsoever on the video... it remains tiny (and as I believe at its original 720p resolution).
I have attached photos of both properties of the clips.
P.S. If anyone can think of a better way of doing it please let me know - All of the source clips are the perfect resolution, can I export the sequence and then import it with all of the source footage at the correct trimming times?
Thank-you so much for any help! This is killing me.