Try this:

Door Travel Adjustment

When closed, the weatherstripping on the bottom edge of the door should be in contact with the ground. If your door doesn't come down that far, you can adjust the automatic opener until it does. Inside the casing of the opener you'll find two adjustment knobs. One controls how far the door closes, and one controls how far it opens. Adjust this knob to lower the door to the floor, but don't adjust it too far, or the door will push against the the top track. If it does, it will bow the track, which can cause excessive wear on the opener.