The way I do this is to have a separate sprite object called scrollObject to handle scrolling, and make a variable to control its x-offset (because it sounds like you want it to be not centered on the cat, but done so that the cat is on the side of the screen). Let's call that variable scrollOffset, and give it an initial value of whatever you want. You'll probably have to try a bunch of different amounts of offset to get it to look just right. Let's also make another variable called scrollSpeed so you can easily change how fast the 'camera' moves over to the cat and give it an intitial value, let's try 5 (again you'll want to test it out). Oh, and let's give the scroll object an instance boolean variable called doScroll, so we can tell it when we want it to do the scroll (initial value false). Then in events:
-on start of layout: set scrollObject X position to catSprite.x+scrollOffset
- cat collides with platform: set scrollObject.doScroll to true
- scrollObject.doScroll is true
------scrollObject.X < catSprite.X+scrollOffset: set scrollObject X to scrollObject.X + scrollSpeed
------else: set doScroll to false
EDIT whoops I'm too late I guess, also perhaps I misunderstood what you wanted