Alex, welcome to the "you're going to do WHAT to me? I think I don't want to do this" club.
Truly, the incision is NOT a problem. It looks awful at first, and sounds horrid, but the consensus of opinion is that abdominal surgery is much more painful. The difference is in the length of time for recovery.
Your heart itself doesn't hurt after surgery. How weird is that? Your chest will hurt, but as said before, they aren't stingy with pain meds. They want you up and walking in a day, and breathing well, so they manage your pain very well.
After surgery you'll be weak as a kitten for much longer than you can imagine. Naptime is mostly any time. If you just go with the flow and accept that you'll be down for many weeks, and do what exercising is recommended, you'll be OK.
Strangely, the type of incision appears to have little impact on how long it takes to recover, unless you need to lift things a lot. This surgery is a great insult to your body however they get into your heart, and your body demands a long time to heal. But it's not terribly painful - unless you cough or sneeze or hit your chest. Then the tears will fall.
I was terrified. My imagination and fears were far worse than the reality of the surgery and recuperation. The bloodwork was the worst and most stressful part of hospitalization. Go figure.
You're in good company. At your age I imagine you'll have a quicker recovery than most of us.
If you find you're terribly obsessed by this and can't sleep and worry all the time, please call your doc and get chemical help - I was on xanax prior to surgery and many of us found this was a great help. There isn't going to be anything in your life much more stressful than anticipating this surgery, so don't feel ashamed of asking for help. It's not good for your heart to be constantly worrying and losing sleep.
Hang in there - and ask away.