The fact that you have said ‘yes’ to something previously doesn’t mean that you can’t still say ‘no’ right now.
If it’s not serving you, if you feel it in your heart or gut, if it’s not aligned with your values …
… it might be better, with the proper amount of respect and notice, not to continue.
Isn’t that better for everyone involved?
If you can’t bring your heart and soul into it, then you’re not really going to be able to deliver the maximum value expected.