Hi Dan,
It is not currently possible to align the image to left or right, it will always display in the centre. On a mobile device this looks good as the display area is narrow so the image take up most of the room, however as you point out on a landscape tablet or laptop screen in full screen mode there will be a lot of empty space either side.
We do not have an open enhancement request for this issue, can I suggest you raise it on the ArcGIS Ideas page for Survey123 so other can vote on it or alternatively raise it via Esri Support as a new enhancement.
Regards,
Phil.