This is my favorite topic. I had a ten pound baby with only a small superficial tear.
Fat is squishy. Babies can be average sized and have a giant head, or they can be ten pounds and have an average head. Ten pound babies are not heavy because they have enormous skeletons, they weigh more because they have more body fat. And fat is squishy. You won't have any more trouble with a ten pound baby than with an 8lb 14oz baby!
My sister just had her third. Her first was 8lbs 2oz. Her second was 9lbs 4oz, and with this baby she was huge, HUGELY pregnant. She really felt that this baby was going to be bigger than her others -- in the upper nine pound range. She just felt more weight and pressure, etc. The baby came four days late (her other two had been a week early or on their due date) and weighed 8lbs 3oz.
So, bottom line:
1. Thinking the baby might be big doesn't mean it's true.
(BTW, my second weighed 8lbs 9oz. I was certain I was having another 10lb baby!)
2. Fat is squishy. Your birth will not be harder because the baby has body fat.
3. Worrying about the size of the baby will only make you worried.
4. A bigger baby can be easier to birth because they don't have room to wiggle around and pick a bad position. They have to choose the path of least resistance.