Strawberry Preserves too runny?

You might not have quite gotten the temperature high enough when you did the final cooking. Strawberries have a natural pectin in them, which is a thickening agent. This gets released during the cooking process and it's what causes jams and preserves to thicken properly when cooled. You might have also used strawberries that had a high water content in them. Still, you might get away with reheating the jam and letting it cook longer, which should release more pectin and evaporate more of the moisture.