the planters are 5 1/2 inches deep and 6 inches wide ... and 3 feet long. I put some old potting soil with styrofoam bubbles (from old house plants) on the bottom for about 2 inches, then i put 1 inch of new potting soil above it and place a variety of snapdragon, bachelor buttons, marigolds, and a wild flower mix throughout the planters, and covered all seeds with another 1/2 to 1 inch of new soil and watered carefully untill completely saturated. .... the question .....I have about 2 1/2 + inches of space from the top edge of the planter to the soil inside... is this too deep? should the soil surface be closer to the top of the planter?

That should be okay, as you want some room for water to stay when you are watering the planter. Also, that will give the plants some stability.