Echoing other's sentiments, you'd be surprised by how low your perceived 100% is when you expand your capacity by taking on challenges. Further too, you never know what opportunities will arise from your life when you say yes to things!
In 2018, a band director approached me to perform keyboards for an upcoming production of Young Frankenstein, because his first pick was unavailable. I looked at the book, which had some complicated areas, switching instruments, and it was just sooooo thick! I got really nervous about my ability to hang. I told him I'd think about it, but as soon as I said it, I knew if I said no, I'd be capping off my own potential, and said yes like 20 minutes later.
While I was nervous, I created a simple daily goal: during rehearsals, play one bar with both staves. This was my goal because in performance situations prior, I would just play one staff with both hands out of fear of making mistakes. As it happened, when you're in the heat of the moment and the music is flowing, you don't just say "Well, I played my one bar, I'll just play one staff with two hands now!"
So what was the end result of me taking on this challenge? I ended up vibing with all of the people in the band really well, and we formed a band that's getting bigger and bigger every year (I moved away a year after it formation, but I'm still really close friends with several of them and get updates from them and see the social media posts).
The band director loved working with me to the point where I became his first pick piano/keyboard player for the rest of my time living there.
I made a connection with the theater owners and producers, and the following year they had a play that desperately needed music, and I got to score it. From then, I became their in-house composer for several years...last year was really dry for me musically, but the income for music I got was solely from the royalties for their theme I wrote last year!
And of course, I now had an irrefutable experience in my life that told me I could take on tough challenges. : )
Obviously, it's your decision whether you take on the gig or not, but it's truly amazing how much the course of our lives move because of one three-letter word.