By example:
Thee initial position of the circle will be {0.5, 0}, {0.5, 0}
The final position of the circle will be {0.75, 0}, {0.75, 0}
The circle, won't "Twin (TweenService)" its size in one direction, instead, it will interpolate its size in each axis, maintaining its position on the center of the screen.
Simply set the AnchorPoint property to the middle of the object.
circle.AnchorPoint = Vector2.new(0.5, 0.5)
This changes where the object is positioned relative to its position.