Don't use Progress Bar object. It's very easy to make a custom progress bar with a sprite or TiledBackground. Simply change its width, for example:
ProgressBar set width to (Self.ImageWidth*progress)
where progress is a number from 0 to 1.
Sorry for a late response! It seems to be kind of working, but no matter what I do, the right side of the progress sprite gets faster than the left side. I used a timer for 5 seconds for this one, and it starts as a 5 second timer, then I use:
System > Every tick > (Progress Bar) Set width to: Self.ImageWidth*GrowProgress.Timer.TotalTime("5") <-- Just a tag
My main effort is to fit the progress bar in the frame for it that exists as another sprite, but it just looks unnatural if the other side gets longer faster than the other one...
I'll be very glad if you help!