Well, I can understand your mixed feelings. They are absolutely appropriate to your situation. However I think most people are capable of being adequate or good parents, and I also truly believe you will feel differently about your child than you do other people's. I've never been a big fan of other people's children but I know I will enjoy my own, and I'll probably end up understanding other people's children better as a bonus!
Regarding telling your dad: I would approach him with a plan. I would say "Dad, here is the deal, and here is how I plan to handle it, financially and otherwise. I'm prepared to accept the responsibility, but I'm also scared at the idea of this and could really use some support from you." He'll be impressed that you are living up to your responsibilities and probably touched that you would come to him for help.