Hi Karen,
For a circular card to be completely circle, you will have to cut the card base as well as a another circle to tape over the card base.
To cut the card base, fold your cardstock in half, line up your die over the fold, making sure you don't cut that all the way. Then adhere your full circle over the card base, covering the fold.
You can see what I mean under Variation in the
Easel Card Tutorial. Just ignore the extra score line in the card base shown in the first image.
Happy New Year!