Increase thickness of non-straight uniform-colored line

[DDer_Joel]

Hey there,
I’ve got a clip that shows a route on a map that I drove. (Like this, 0:13 https://youtu.be/fafAm0q3He8?si=BmSSUo53Q6cOGYko&t=13)
The route is in a uniform color, but I’d like it to be thicker.

I can so far played around with the filters (Key Spill: Advanced, Choma Key: Simple, and Mask: Chroma Key) to isolate the color of the route, and I’m able to make it transparent such that uniform-colored plane from a track below shines through.

Now my question is, how can I make this key/selection just bigger.
I am thinking of the GIMP steps of “Growing a selection” and then uniformly coloring it.

I hope it makes sense what my problem is, please ask if not. I’m happy to provide the clip / screenshots, etc…

[shotcut]

Maybe Alpha Channel: Adjust Video Filter

[DDer_Joel]

Cheers!
Ended up putting a blue background to V1, then put the clip into V2, and add “mask: Chroma Key” and “Alpha Channel: Adjust” to V2.
Mask: Chroma Key has the key color as the color that the original line has, the distance ended up being 32% for me.
The Alpha Channel: Adjust has the mode of “Grow Hard”, which an Amount of “100%” and Invert.

See before and after: