I think you're right in that we operate our lives based on our true nature. This doesn't mean, however, that we do not have free will.
We live our lives according to our basic nature. This is the Big Picture....from birth to death. We are born with certain tendencies dictated by our genes....(or some might say our Sun Sign. :-)
But, our environment, family, friends, and experiences will help develop our personality and will eventually influence our choices. This is the details....(or some might say our Moon Sign. :-)
Now, let's use the metaphor of Adam and Eve. What if the temptation offered to Eve to indulge her desire to eat the fruit was actually God's "gift" to mankind. Up until that point, Adam could only be like God, because he was created in God's image and was perfect. There was no disobedience in him. As long as there was no influence to sway him, he didn't have any choice but to be who or what he was.
However, when Eve was made for him and given to him to love and care for, he now had something to factor in when making choices. Her influence changed his Personality. By choosing to please Eve rather than God, Adam implemented Free Will. From that day forward, man became separate from God, developed an ego, and thus free will was born.
So, in a nutshell, even though I have a genetic tendancy to be a certain way, my self-discipline which I learned from my parents, my experience with a particular life-changing event, the example set by a friend I admire, or my overriding love of my partner, will factor in. Now, do I follow my tendancy or do I make another choice based on all the influential factors? It's my free will, my choice.