I am glad you used potting soil. That should be more than enough to maintain moisture. Do you mean that your raised bed didn't get filled up to the top of the sides? Potting soil is exactly what you needed to use. Potting soil has very little actual soil in it, is that what you are worried about?
You have no worries about holding onto moisture. You do not want to add garden soil with clay, or any water holding sponges or gels. I would use decomposed compost to mulch around your plants on top of the potting soil. Make sure the compost is not manure based; too much nitrogen for your plants. Do use extended release balanced fertilizer for vegetables.
Being in Florida I would also have a 'shade' cloth, its black and only 10% shade mesh would be necessary for extremely hot days (over 85 degrees F) to cover. Even the white floating row cloth would work as a temporary cover for excessively hot days. When the wind gets blowing I would also cover my plants with either fabric.
Water well before planting starts. If you plant seeds do not soak the soil deeply, just the surface needs to stay moist until the plants have some height on them and deeper roots. Then water deeply and allow the top inch or two to dry before watering again. The plants themselves will help shade the soil when they mature.