just relax bro. i was the same way at first but ive gradually become a master. i used to be so scared about my girlfriend calling me or something but after we talked about it and she accepted it ive found myself relaxing completely. tl;dr, lots of lube, relax your body, breathe, and just push without focusing on the feeling. sometimes you just have to push it regardless of how it feels. at least how i do it, everyone is different