[JRTJH]

If it is sliding fore/aft adding a screw will help stop it from sliding and possibly stop it from coming out of the track. I wouldn't imagine that's the issue or the entire awning fabric would be moving fore/aft and you didn't indicate that it was. Adding another screw won't secure the fabric in the track, it would only keep it from moving fore/aft not keep it from pulling out of the track. I'd suspect that the track slot is somehow opened up and is just "too wide" which allows the cording to pull out.

During assembly, almost all factories use a tool to widen the slot at the end so the awning fabric can be slid into the track. Usually (should be always) that slot is squeezed shut before the locking screw is installed. It sounds like the slot wasn't squeezed shut on your trailer.

If you can push the cording back into the slot and squeeze it shut, you should have the problem resolved.