How large were your pans?
Do you have the recipe somewhere? How much flour and starter did you use?
One thing you could do with loaf bread is bake it at a higher temperature for part of the time and then remove it from the pan and finish baking it on a stone (or cookie sheet) at a lower temperature so it bakes more evenly.
I've had my dough spill over before, too - but didn't have a density issue with it.