I started a new garden bed and it seems after I till the area, the place I marked where I want the bed is all covered with soil making it hard to see the line. Does anyone have any suggestions on how to avoid this. Thanks
You could mark outside of the garden area. If visual cues weren't enough, marks would allow you to install stake & strings after tilling and re-establish exact edge.
If curved, mark a duplicate edge outside of the garden with a uniform offset--like 2'--so that original edge can be re-established.