I just did this the other day and used a 9x9 pan. It came out fine and I'm sure the 8x8 pan would, too.
Your pan being smaller, would make the batter a little thicker, so as others have said, just make sure
a toothpick inserted in the center comes out clean and you'll be all set.
DISCLAIMER: The messages on this forum and any links to external websites posted within the forum express the views of the respective authors. They do not necessarily represent the views of the administrators or moderators. Any advice posted here is for support purposes only. It is not intended as a substitute for advice by a qualified health professional.