Looks like you have some anamorphic sd footage.
right click the imported file, interpret footage.
set pixel ratio from 1.0 to 1.2
It will letterbox it in a 4×3 (720×486) sequence.
or export it with media encoder set that way or leave it as is the way
you already have it now but change the pixel ratio for 1.2 on the export screen.
I’d recommend exporting it as 853×486 with a pixel ratio of 1.0 if this is
for youtube or vimeo, they don’t usually interpret the pixels properly