I hope you and your therapist are exploring what "I can't" means and what saying "No" means. Saying "No" is a way of saying "I do have a voice". Saying no is a way of saying 'I will think for myself', 'I will do what I want', and on the surface it may sound obstinate and negative, but underneath that there are other things going on.
My therapist has suggested that it's a way of being heard, a way of fending off engulfment.
We have also explored the idea of going along, and have thought together about what that means and what it means to not go along.
We've also explored the fears associated with trying things I want to try, doing things I want to do - the fears that can seem small but can be huge roadblocks to what we want.

So there is a lot to learn. We are complex, thoughtful people and not Pavlov's dogs. When it is the right time for you to take risks, you will. You may still have some fears and uncertainty, but you will be able to when you are able to. There is no judgement or pressure to perform.