How can I get him to like the Ergo?

My mom was kind enough to buy me an Ergo Sport during my recent visit home, but Elliot screams when I put him in it. He is 3 months and a pretty big boy (14.12 at 2 month check up and 24.5 long) with great neck control, so I didn't get the infant insert. He seems to fit well with his legs spread but I was worried this is why he was crying, so I bent them up, tried one leg in and one out, a folded up cloth diaper under his butt... but he still screamed. I have tried several times over the course of a week with no success. Should I keep trying until he learns to tolerate it or put it away and try again in a month or so? My mom bought it at REI with a rebate check and they don't sell other brands so I can't really exchange it, and it's so comfortable on me that I want him to like it. Any Ergo users have advice as to when their babies started liking it? He's a fussy boy in general who seems to hate everything except being held and riding in the stroller.