Day 3: Looked like there was almost a 50% rise and it had fallen. I could see the line it rose to. I gave it an extra 12 hours, but there was no further rise.
If you could see from the line that it had doubled, and then gave it another 12 hours, your starvin' the poor thing
As Audrey II said "Feed Me Seymour!"
Toss half and keep feeding. It can take more than 2 weeks to get a starter strong enough to build a dough with.