How do I create a simple progress bar animation?

I want to create a simple progress bar filling animation.

I have a zero hight sprite that i use tween to increase the height (in the hopes it would look like a bar filling) but the height is increased to both sides of the sprite - thus out of the bar itself (see pic, the yellow part starts in height 0 and increased to 100).

Any ideas how to achieve the desired result as simply as possible?

Thanks

Lower memory footprint by having a smaller pixel size of the source texture. Looks better when "scaled".

Honestly pretty negligible relatively speaking, but it definitely has merits as a "best practice".