Im having a kid and I'm scared absolutely shitless. I guess moreso about being responsible for this new humans upbringing and the possibility of failing and destroying an innocent life.
If you search your soul, you'll find that the true cause of your fear is the fact that you will have to give yourself, truly and utterly, to the concept of unconditional love. The rarest of all forms of emotion, I believe.
Few men truly, and unapologetically, love their wives unconditionally. After all, if she cheats on you, wouldn't you divorce her? Hence, you do not love her unconditionally. Your love for her is based on her ability to remain faithful, for example. A condition.
Love for children from capable parents knows no such bounds. I love my children unconditionally. There is nothing they could ever do to change that. Nothing at all. Come up with the most ridiculous, barbaric, out-of-this-world thing they could do to make me hate them, and I couldn't it. I will always love them. They could fire a shotgun into my face and I would love them with my dying breath.
Giving yourself over to unconditional love is truly scary. It means you no longer have control of your emtions. You now realize that a great portion of your own happiness depends greatly on the success and happiness and health of your child. As your child goes, so do you. Therefore, their very existence has the ability to enrich yours, or tear it to pieces if something happens to them. That is truly scary for the primarily narcissistic male (which, as bodybuilders, most of us naturally are). Good luck wrestling with those emotions.
It will not get easier. But, it is what it is.