Thank you so much, that solved the problem!!!
You're welcome. Hope your photo processing goes well for you.
The Post-Crop Vignetting panel is worth some experimentation time. You can really achieve a wide range of effects by manipulating the sliders.
Solid black or white borders come from Amounts of -100 or +100, and the rounded corners on the preset you showed, as well as the width of the 'border' come from the Midpoint and Roundness sliders. The feather at 0 is what made the edge sharp.
In any case this adjustment is a way to get a simple border inside Lightroom without resorting to taking the image out to something that understands layers like Photoshop or other applications that let you stack a border on top an image layer.