How can I stop flinching?

Every time I'm in a spar, I always find myself flinching and unable to move forward and do several combos. I don't know if its because I don't want to hurt my partner or if I'm subconsciously scared of getting hit. My build is more of an in fighter but I always find myself sniping a jab and then backing off. Is there a mental exorcise that I can do to keep going? Or do I just have to keep practicing to move forward?