Of course I don't know your sins. But I think in general christianity makes people feel that they're sinful, even though that's not always the case.
Anyone who professes to be a Christian but who does not espouse the biblical teaching that people are fundamentally sinful is not taking a truly Christian view of human nature. The Bible is very clear about the tendency toward evil that is the common denominator among human beings. And this is borne out through all of human history.
To make a mistake every now and then isn't evil. That's human. I sincerely doubt that your sins are as bad as murder.
God doesn't condemn "making a mistake" when it is something like forgetting your Mother's birthday or rear-ending someone on an icy road. Sin, though, isn't merely "making a mistake." Not as far as God is concerned. The heart of sin is selfishness, putting the interests and desires of a finite, ignorant, dependent creature before those of the Almighty Creator and Sustainer of the Universe. The hubris, and myopia, and foolishness of such behaviour is staggering! Human selfishness has caused incalculable destruction; it has produced corruption and death; it has burdened the world with sorrow and tragedy beyond telling. No, sin is definitely not merely "making a mistake."
You are quite correct in saying that sin is human. And you don't need the Bible to tell you so to see that it is so. Oh, we like to downplay our wickedness, make it seem as small and innocuous as possible. But this is just our pride and self-centeredness rearing its ugly head. Who wants to admit that they are sinful? Who wants to confess to wrongdoing? Who wants to concede that they are wicked? No one, obviously. Instead, humans offer up all sorts of justifications for their sin. Many go so far as to suggest that
God is the One with the problem, not humanity. He over-reacts to our "mistakes." His anger at our sin and judgment of it is outrageous! He should relax and take a more magnanimous, human view of sin. Again, this is simply human pride and self-centeredness attempting to justify itself. And it does a pretty good job. Few people believe they are the sinner God says they are. God is inexorable, however, in His hatred of our sin. He will not be dissuaded from His wrathful judgment of our wickedness no matter how persistently and vigorously we dismiss Him as a figment of imagination, or the vestige of primitive thinking, or the crutch of the weak-minded.
Galatians 6:7-8
7 Do not be deceived, God is not mocked; for whatever a man sows, that he will also reap.
8 For he who sows to his flesh will of the flesh reap corruption, but he who sows to the Spirit will of the Spirit reap everlasting life.
Hebrews 10:30-31
30 ..."Vengeance is Mine, I will repay," says the Lord. And again, "The Lord will judge His people."
31 It is a fearful thing to fall into the hands of the living God.
Selah.