You are OK with that score. 8 pull-ups is low, but not failing. You want to have at least a 250 to be comfortable. Pull-ups are where you make you money with five points a shot. 20 is ideal but if you get 12 to 16 you will be alright.
They just take a little effort to get good at them. You really don't have to get stronger you just have to practice. Five sets of five for four days and max set on the fifth.
It takes a little effort to get used to pull ups, but once you go to OCS, TBS, then the fleet you will recognize that they are part of being a Marine and it will soon be second nature.