Then cut and install 1x3 fascia over the 1x4 fascia. Use treated lumber for the corner boards since they're in ground contact. Cut the corner boards to size and nail them into place with 8d nails.
For the back, we used all 1x4 boards and copied the same angled pattern we used on the arms ... but if your swing will be in the weather a lot, you might want to consider treated wood or cedar. Next ...