Making Sour Dough from Starter
It sounds like you're making something closer to a barm. In "The Bread Baker's Apprentice", Peter Reinhart recommends making a 'Barm' using by weight, 7oz starter, 1# each water and flour. His starter is .5 cup water and 1 cup flour daily and discard half.

He uses the barm to make a firm starter ( 4oz barm, 4.5 oz flour, 1-2 oz water). Let this rise for 4 hours and refrigerate overnight. Add 20.25 oz flour, .5 oz salt, and 12-14 oz water. Kneed together and let rise for 3-4 hr, proof and bake.

You could just add more flour and you'll be fine though, or reduce the water some AND add flour. It wouldn't hurt to increase the percentage of the starter in your final dough to closer to half the weight of the flour. 

One thing to know is that the ratio of water to flour in your starter will affect the ratio of acetic acid bacteria and lactic acid bacteria. Acetic acid bacteria prefer firm starters, so if you prefer that flavor, adjust the hydration of your starter.