That's my understanding on this as well. Predestination exists but so does free will. God gave us free will on whether or not to believe the Gospel, however if he knows what choice we are going to make anyway, then how is he giving us free will to choose to accept. But He does know and He is giving us free will at the same time. Makes no sense at all to our minds, but the things and ways of God are not the things and ways of man
Personally I've never truly understood all the hoopla around free will and predestination myself. If I witness to someone and they choose to accept the Gospel of Christ down the line, was I destined to witness or not and were they destined to accept or not? Never really did care. I was carrying on the commission as the Bible teaches us to do, so what does it matter one way or another if it was predestined