Starting seed culture... need help

Hi,

I just started making my own seed culture following Peter Reinhart's (A Breadbaker's Apprentice) receipe. It was going fine until the Day 3, where i got maybe 30% rise instead of double, I waited another 24hrs and still no luck. So I went ahead and discarded half and mixed my seedculture with the Day 4 ingredients. And after 24 hrs... no rise. 

My apartment is pretty cold so at this point i poped my seed culture in the oven with a bowl of hot water. 

Do I need to restart my seed culture and watch the temperature this time? or just wait until it doubles in size to start the barm, and if so, should I keep discarding the half and add the Day 4 ingredients to the existing seed culture?