Everyone around me seems highly competent and more in favour with the boss.
Remember that a part of their mind is making them think that when they look at you.
My first introduction to impostor syndrome was at a work 'stress management' event. I poured my heart out to one of the facilitators in the bar in the first evening about it. He said, yeah, we all have that, siht isn't it and carried on.
Anyone I have got to know really well has at least a touch of it, men, women the lot.
In my experience, the more confidence people appear to have, the more likely they are to have some doubts which they keep well hidden. No one seeing the me I present to the world me would ever guess
You can relax about it, honestly and find what helps you ignore it and annoy your success. I need feedback from my role so I have some evidence that I am well thought of. I need people who understand the role who can help lift me up when I feel particularly useless and for whom in turn I can do the same.
The most helpful thing for me was to get to know a colleague in a similar role who I know well enough that I can see when something knocks her and she starts sliding into that pit of despair. We have now seen each other do it often enough that just know the other understands can be enough to recover. Being able to say honest when ... I found myself ... is also a great relief
I hope you find what works for you. It really is fixable and I would say that you owe it to yourself to work out what support you need. Not easy but v v simple.
@NurseButtercup has it absolutely.