Showing an example of how to inpaint at full resolution.
Using masquerade nodes to cut and paste the image.
The width and height setting are for the mask you want to inpaint.
Padding is how much of the surrounding image you want included.
Note that image to RGB node is important to ensure that the alpha channel isn't passed into the rest of the workflow.
If the pasted image is coming out weird, it could be that your (width or height) + padding is bigger than your source image. Change your width to height ratio to match your original image or use less padding or use a smaller mask.