Doesn't sound good. Sounds like the slide is going out too far.
Can you give us any guidance here on the slide mechanism style? You mention a chain. We have a number of manuals under Tools - Manuals from the navigation bar at the top of this page.
Also, take a quick look at Lippert's website to see if any of these are what you have:
https://www.lci1.com/support-slide-outs/
Skip over any that are hydraulic. Once you identify what you have, we can jump back in and possibly help you.
Also, before you run it out again or sit in that slide, please call Heartland Customer Service in the morning at 877-262-8032 to seek some guidance. They should be able to tell you what you have - so that's a start. And they may be able to give you some direction on adjustment.