How to show one variation of one product in a View Pane
If what you're seeing is the fully rendered Add to Cart form in your View, then what you're looking to do is impossible without custom code. The Add to Cart form is rendered via the field display formatter on your product display node type. It has no way to interact with the configuration or results of a Views query.

You can create a View just showing variations with an Add to Cart button that doesn't invoke the entire form, but doing so will strip the creating line item of the context of what product display that variation is a part of. This means the line item won't link to the product page like it ordinarily would. You could always link it yourself if you know that each variation only exists on one node via a reverse reference, but you'd likely still lose some functionality related to the standard form's normal grouping of variations.

If that's an acceptable trade-off, then you need to recreate your View using Commerce Product entities as the base as opposed to Nodes. Otherwise you're going to have to create some custom Views plugins.