Your one-sheet headshot has two controls. Neither one can break the page.
The one-sheet editor has no crop handles, rotate, or filters. You drag to set the focal point and slide to zoom. Here is what that means for the photo you pick, and what the upload accepts.

You upload a headshot to your one-sheet and look for the crop handles. There are none. No rotate, no filters, no corner you can pull. It reads like a missing feature.
It is a choice, and knowing the reason makes picking the photo easier.
The frame never moves
The editor gives you two controls. Drag the preview to set which part of the photo stays in view. Pull the slider to zoom between 1x and 3x. That is all.
The frame itself comes from your template. Some layouts crop the headshot to a circle, and the preview in the editor takes the same shape, so what you see while dragging is what an organizer sees.
The point is that the page is shown to strangers. A speaker can stretch nothing and push nothing out of place. You decide what is in the frame. The frame stays where the template put it.
Pick the photo for the frame
Zoom only goes in. At 1x the photo fills the frame, and there is no setting that pulls back to add space around you.
So the margin has to be in the photo before you upload it. A headshot cropped tight to your face is the worst case. Put it in a circle and the forehead and chin are the first things to go, with no way to get them back.
