In your capx do the following
Instead of :
set width: Sprite35.Min+1+experience.nextLevel
set width: Sprite35.Min+1+((experience.experience/experience.nextLevel)*124)
This way sprite35's width will always go up only to 125 and the width will be (nearly) proportional to the fraction of experience you have out of total needed to level up. So it will increase slower with each level (assuming experience gained from defeating foes stays the same).
Also you can use a 9-patch object for an experience bar as it can be tiled easily/expanded easily without stretching it so it can look prettier.