I wonder if this sentence I wrote is lexicologically sound, or if not, I wonder what you’d have said instead

こんにちは、そしてクリスマスおめでとうございます！

They call me Haru! I have been slowly but surely teaching myself Japanese through several methods, and I have just sent a sentence to my boyfriend through FB Messenger while we were just goofing off, which I will copy-paste here shortly. I have three questions about what I had written him, which are as follows.

> 亡いござるに見せかけるをは捕食者防ぐの場合だけ効くんだろうと思ったんでし、おれは捕食者じゃないなんてさ\~

I meant it to say: “I thought playing dead was only effective against predators, and I am not a predator,” with emphasis on the word ‘not.’

Here are my questions.

1. Did I generate that in my head adequately before I sent it to him? Does it make sense to you?
2. If you would have said it differently \[in Japanese\], what would you have said instead?
3. Is there a way to shorten sentences like these? I only ask because, when I tried to read it back, it was quite the tongue twister with ござる and だけ throwing me off.