I’m not qualified to give medical advice, but with injury concerns you should always err on the side of caution, and either take a break and/or reduce the intensity or duration of your workout. There may be some soreness, but real pain from only manual stretches is a big alert that you may be doing something wrong.
In my opinion though, I think if you had a torn ligament you would be in a great deal of pain, and stretching would not just be sore, it would be impossibly painful to even think about, let alone attempt. You’re doing an exercise that is brand new and your body’s under some stress. Just like if you weren’t a runner and went out and ran 10 miles, you may be able to do it, but your body’s going to let you know the next day that you overdid it. Everyone wants to do more, and get faster gains, but that’s usually counterproductive in the world of PE. It won’t take much at all when you’re starting out to make progress, just take it easy to start. Maybe take a day off or two, and then start back with a significant reduction in force or time of your workout, and then gradually add more time and force as you are able.
You never want to be at the point of pain, some soreness perhaps, but not pain.