Fixing embroidery mistake

[LIEN NGUYEN]

Hi, 

I've been struggling with my machine tension and the bobbin thread sometimes shows on top of my embroidery, and I only realized after the embroidery is done. I was thinking of going back a few stitch and cover the white bobbin spot with a new layer but that leads to another issue: how do I tie the knot once I want to stop stitching because I only need to cover a very small stitch, I don't want to keep embroidering until the end if that makes sense. If anybody has experience with this please give me some advices. Thanks in advance.