I think you can truthfully say that you do not believe that God would want you to take this position. And even though you cannot articulate well the reason why not, you feel that it would be wrong to accept, although you do appreciate their confidence.
Whatever line you decide upon, you next need to be prepared to keep repeating it and saying, "I'm sorry. I really believe that this burden privilege at this time is not what God Jehovah desires for me." Don't say anything like "maybe" or "if". Just repeat, "I'm very sorry." "I'm sorry, I really cannot accept the position."
After a while, they will give up. Your dad might give you the hardest time, but maybe you can tell him that since you were told about it, you began to pray about it. And though you can't explain well, you are certain that you are not making a mistake in your answer.
Hope those might help!!
bebu