If the Devil is the Great Deceiver, how would I know that he's not deceiving me through Christianity?

I've always been a devout Christian, but I once had a terrifying thought while reading the Bible, and I'm scared I'm going to go to Hell. At one point I began to question why God killed so many people throughout the course of the old testament, how he killed peoples' first born children, made people give their kids as sacrifices, flooded the entire Earth and killed almost everybody and everything, sent plagues upon people, burned down their cities and often commanded genocidal wars. God also commands that everybody fear him and worship him, lest they should burn in Hell for all eternity. Then, it occurred to me that the Devil is almost never mentioned in the Bible. He certainly isn't credited with killing very many people. He might actually have only killed about ten people in the entire Bible, if I remember correctly. Certainly nothing compared to the millions of people that God kills. The things the Devil really did wrong were deny God as his king and try to give Adam and Eve the Knowledge of Good and Evil. I get that, but why is God the one discouraging knowledge? How could Adam and Eve have known it was inherently wrong to disobey God without having first HAD the Knowledge of Good and Evil? Why is it that God didn't want them to have that knowledge? I remember in Sunday school they referred to the Devil as the Great Deceiver. If he truly IS THE Deceiver, then wouldn't it stand to reason that his deceptive powers would be vast? His capacity for deception would be unparalleled? Could he go so far as to pretend to be God and convince the majority of the world's Christians, and maybe even Muslims, that he IS GOD? Could he convince people to lead crusades and inquisitions? Could he have guided the hand of man to have writ the Bible (and possibly the Qur'an??) for the purpose of striking the fear of Hell into the heart of man and ensuring a future of war and death? To convince everybody that they were wretches without HIM? To make everybody feel ashamed of their thoughts and emotions? Could he have convinced people that knowledge was evil? I guess what I'm asking, from a vulnerable position is, could God as he is described in the Bible, actually be the Devil in disguise? Why would a loving and all-knowing God be trying to convince people that they should shun and hate gay people or people of other religions? God actually commands people to kill people because they are of different religions or races at different points in the Bible. I didn't want to end up hating God as I read the Bible, but by the end of it, I'm afraid I kind of developed a disdain for Him. Even the New Testament, with its morbid demise of Jesus Christ and its prophecies of Revelation, all just seems to be designed to terrify people and make them feel bad about themselves and make them look forward to nothing but a future of fiery apocalypse and uncertainty. It all seems to be designed to make people think they are bad people if they don't follow God's code of law. And then I look around me and I see how hateful most Christians are toward people that are different than them and I assume that the Devil's deception must be working. One day, when the Revelation comes to fruition, and some evil politician wins the Christian vote because he claims to be Christian, I'm afraid it will be the Christians that first follow him right into Hell. I'm afraid I'm already seeing this happening in society today. I'm a Christian that is afraid he has discovered a terrifying underlying message inherent in the Bible, and I hope I'm wrong. Can someone weigh in on this?