Replace the comma after me with a period or a semicolon.
It’s is not the possessive form of it; it’s is the contraction of it is.
I dropped in my mind because those words are unnecessary; they clutter up the sentence and disrupt its flow rather than adding anything to it.
I instinctively knew it was there to take me; I had no question of its intentions. I was completely terrified.
I am very much not a fan of people who parrot “Show, don’t tell!” at every opportunity (“Don’t tell us the character drove a blue car — show us!”), but some sentences really are written with too much telling/not enough showing for the purpose they serve in the story. The example sentences here are all telling. This works if the character is actually telling someone about this event well after the fact and just wanting to sum up what happened without making the listener feel the terror they’d felt earlier. If that’s not the case, there needs to be some description of what “completely terrified” looks/feels like.