What Dropkick, MirrorTodd, and remarkal3le said. I made the mistake of trying to cram too many in and killed myself...thus here I am in the Caribbean (while it's a fairly good school, I'd prefer to be in vet school in the USA)
I'd add them in slowly-one or two clubs that meet like every other week, and then like a volunteer/community service thing (I don't know what you guys need...I'm guessing here)
If it comes up in interviews just be honest. Say "I wanted to make sure I adjusted well to being away from home and the more rigorous academic environment, so I decided not to join any groups/teams freshman year until I was sure I had my study habits down pat. Then I decided to add the activities in one at a time to make sure I didn't overdo it" And let your stellar (hopefully) academic record speak for itself. Don't commit academic suicide like I did.