Not sure I understand entirely, you might try
1) Start with a new project
2) Set project aspect ratio to 16:9 by Edit > Aspect Ratio 16x9
3) Import clip and move clip to the timeline
4) Right Mouse button click on the clip in timeline and try "Set Clip Attributes" > "Set Aspect Ratio" > and then select the 16:9 ratio
See if that works for you.
Jeff