Cruel? Of the places to be stabbed, the belly is probably one of the least severe ones, especially on males, so long as you get medical attention. Stabbing in a limb could result in long term damage much more easily.
You were in the process of being strangled, even if in hindsight you think you did, you weren’t making a choice with any thought of it being cruel or not. There was likely adrenaline at that point, and panic. No one could successfully argue you had the presence of mind to make a conscious decision to be cruel.
I’m sure you’ll have lifelong trauma, and might need to seek therapy if you aren’t already receiving it. It sounds like a part of what you’re experiencing is a form of survivor’s guilt. But no, how you got yourself out of that situation wasn’t cruel.
You might tell yourself in retrospect that you consciously made that decision to deepen it and twist it, but with the adrenaline, panic, fear? You instinctually reacted to survive, and the fact you were able to withdraw from the situation before inflicting greater harm is a testament to the fact it wasn’t cruel.