Seems like when I 'render in to out' I run into this issue where my video gets stretched and you see the black bars on the side.
Question from user requiemfad123 at premiere at reddit.
When you export, in the video size select match source (or maybe its called match sequence settings).
That should respect the original sequence size.
Even once that is selected, you can change the size and as long as the lock icon is activated it should respect the proportions.
Answer from user Powerful-Employer-20 at premiere at reddit.