If you are having these feeling then postpone the appointment. I understand logically that you don't want to have more children. But if you are suddenly having doubts it does not mean you think you want more, it just means that you don't want to have the choice taken away yet. Try using the Nuva Ring for a while, it inserts int the vagina and stays for the 3 weeks then it's removed. After a week a new one is put in.
It is low dose and doesn't go through the whole system like a pill does. If intercourse is uncomfortable while it is inside then it can be removed then put back in afterwards.
I have 4 friends out of 5 who had procedures done to stop the possibility of becoming pregnant that regretted it afterwards. They realized they would never feel a child inside them again, they felt barren, didn't feel feminine and fertile anymore. It should have been put off for them. One friend had her hubby get fixed when they were done and then she regretted it and divorced him so she could get pregnant again. She had several more children with the new hubby. The one that is happy she got fixed is now going through a divorce and the hubby's girl friend is pregnant.
Since this is not a required surgery I think waiting a few months would not hurt. In my honest opinion if a woman reaches the point she is done having kids then she is the one responsible for have any procedures done. It is not anyone else's responsibility.