How to stretch image section

[enginestar]

Can someone tell me how to stretch an image section.

I've tried and am failing. I'm using Gimp 2.10. I can't get to grips with the controls.

I make a selection and then use the Scale Tool to stretch.

Great. Except...

- When I click away I find it hard to unselect.
No matter what I do, the white ants STILL surround.

- When I click away, the bit I had stretched, no dissapears!

- Sometimes I managed to succeed (somehow!!).
But then a line 2 pixels are missing - why!!!?

What am I doing wrong?

What I want to do is a 60 second job.
I've trawled through youtube videos - I cant find any dedicated to what I want to do.

What I want to do might be there... but it's in the middle of a much longer video!

Any pointers would be great.

Just to illustrate, take the pic below. Say I want to stretch the right hand said and make it similar length as the left side.
(Doesn't matter if the right side looks stretched and odd - just using the pic as an example, nothing else.)



Thanks.

ACTUALLY...
Something else... to try and achieve a similar effect, something I used to do in Photoshop was copy the right section, flip it so it's the mirror and then join on the right. If the image is blurred, this helps extend and not look odd. How could I do this?

Double thanks if I can get an answer to the above. ?