If my sin is not by my free will choices rather than an inborn sinful nature, then explain why Adam sinned in the first place.
Adam and Eve, had free will no one argues about that. The problem is not physical freewill but Spiritual freewill.
You are free to buy whatever car you want, what house to buy , how to spend your money.
Yet because of the Fall you are naturaly against God, the Human nature has changed. your disposition is towards a sin nature not a glorifying God nature. we love the darkness and not the light.
This of course does not mean we are all as bad as we could be, some murder some rape, others constantly tell lies, adultery etc etc, you have to remember that we are dispositioned against God. so all your choices although your own choice are not totally free, why is this.
because you are a slave to the world, you thoughts are of carnal things, so your 'free' choices spring from a carnal nature.
And if you say my choices are not based on a carnal nature then you are full of pride and thus making that choice from a carnal nature!
Now that you are in Christ, you are a slave to Christ, your thoughts should spring from this new nature that you have been given by God, so although your still free to choose, your choices will spring from the goodness that is within you, fruit of the spirit and if you don't you have an advocate Jesus.
This is the big mistake people have about the reformed position regarding freewill, we believe you have free wil, but it any choice that you make springs from either a carnal mind or a new regenerated mind in Christ.
So although you make the choice.. this choice can only stem from your nature, that is either sinful or regenerated.
hope that helps to clear things up.
Thats why I cant believe how many people attack Calvinism, yet they don't really know what it is.
you have freewill but your choices will always stem from your nature or who you are.
to put this simply.
If you are not in Christ your choices will come from a carnal mind you are a slave to the principalities of the world.
If you are in Christ your choices will flow from the renewed nature in you, the power of the Spirit will guide you.