I work in the same industry as you and the buck stops with me.
I remind myself that making any decision is better than no decision, and that usually there is no such thing as a wrong decision anyway. Just make one and execute it with your full energy and conviction. I’m also fully prepared to deal with the fallout if it was a bad decision and it doesn’t scare me.
I lean a lot on data and scoping and won’t make big decisions until I feel I have the information I need.
I also remind myself that it’s just marketing. No one will die. How wrong can it go?
if people disagree with me, I listen. I like to have my mind changed, it’s good to learn from other people, one human can’t possibly know everything. If they don’t change my mind, I will just restate my position and why I reached that decision, and let the team know that I understand it’s on my head.
I have one colleague that I often bitterly disagree with and it can get very heated, but we ultimately have a huge amount of respect for each other. If we clash, we retreat and cool off then have a more respectful conversation and find a middle way.
To find my inner confidence, I have a professional role model. I ask myself what she would do? She’s bold and confident and seemingly fearless, direct without being aggressive - i pretend I am her when I have to. Fake it til you make it.