Remember, children always inherit the size of their parent object! So, to make it match exactly with the Container's size, you actually DON'T want it to have the same scale values.
Children also inherit the position values of their parent object. So, to make it match exactly with the Container's position, you don't want it to have the same X and Y coordinates. Instead, the HealthBar's X and Y positions should both be 0.
Instead, go into the Health Bar's properties and find the "Position" property. Open it up to find the X and Y values. Type in "0, 0" for both X and Y.
Inside the HealthBar's properties, find a property called ZIndex. This is the Z position, or the depth of the HealthBar. (Or, how forward and backwards the HealthBar is.)
To make the HealthBar appear more "forward" or on top of the Container, set the ZIndex to 2.
Near the top of the HealthBar's properties, find the property called BackgroundColor3. Click on the little square to choose a new color for your health bar!