1. I can't do it right now, but maybe later.
2. Unfortunately, I've had a few things coming up.
3. I'm trying to focus on finishing off something.
4. Sorry but that isn't my strong suit.
5. I'm sure you will do fine on your own.
6. I'm afraid I'm in the middle of something.
7. I can't help right now, but I'm happy to help you with something else later.
8. I really don't enjoy that kind of activity.
9. I'm sorry, but I have an emergency to attend to.