Wow. It's been 4 days and because the fish isn't fully acclimated and aggressive enough for your standards so you think you can just get rid of it?
What happened to patience? I mean honestly, that's pathetic. Just because you've grown up in a world where you've known nothing but instant gratification through the internet, tv, and whatever else doesn't mean patience shouldn't count for anything. If you really did have intentions of returning the fish because it's not chasing your fingers like a mad man in 3 days then do both you and the fish the favor and find it a GOOD home; then get rid of your tank if you're not willing to be a responsible care giver for A LIVING THING. The fish is not just 20 dollars worth of entertainment that you keep in a glass box with water.
What's going to happen when you're an adult and you're banking on a boy and your wife pops out a baby girl? Are you just going to shove it back in there and say redo? I mean really dude, anticipating and expecting certain behaviors or personalities from any living thing is just naive and silly.