Don't stress yourself too much. It's good to be aware of all the possible outcomes but as long as you don't do or say anything stupid (yes, that case from above!), you will be ok. Now, from personal experience (my POE was Dulles in DC), they brought me to the secondary which is normal at that airport (or maybe was, not sure), the officers asked if I had a return ticket which I didn't need to so I said "no, we will be building our life here", they laughed and told me to sit down. 10 minutes later, they told me I was good to go. Just do as they tell you and you'll be ok