It's always wise to never have your jar more than half full of unfed starter because it needs room to grow after feeding and you don't want it to overflow. In most instances with this recipe, and as long as you used a 1 litre or larger jar, this shouldn't happen, but in the rare event it does, simply remove most of the starter from the jar, just leaving a little bit at the bottom (even as little as a teaspoon is fine) and start feeding that small portion. Or transfer a small bit to a new clean jar and start feeding it there. The excess starter that you removed can be composted, added to the dough of a regular yeasted loaf, pizza dough or used to make pancakes or waffles.