Feeling scared you won't be able to handle a situation like this is very normal, especially the first time you are confronted with such a situation. Crying is also normal, and healthy.

I agree with others that these thoughts are compassionate. They are also honoring and respecting you mother's wishes, which is important. Have you looked into hospice care yet? That sounds like what your mother and family need. Hospice isn't a place, but the idea of making the end of life as comfortable and peaceful as possible. Sometimes it involves being in a special facility, but sometimes the patient can stay at home, and the hospice team assists in whatever ways are needed.

Death of a loved one is always difficult, and the first one is even more difficult. It is your choice whether or not to talk more to your therapist about this. It is not obligatory. Whatever helps you get through this difficult time is what is best for you. Talking with other family members and your mother's friends could be helpful, possibly even more helpful than talking with a therapist, since they know your mother and this is a shared experience.