Yogurt: A Failure

I tried to make yogurt, and I fucked it up big time. It came out curdled and watery. I think I added too much starter to the milk, and I don't have a thermometer to get exact temperatures. Heres how I did it:

1 quart whole milk, 1/2 cup plain yogurt. I heated the milk until it nearly boiled, let it cool down until it was just a little warm. Then I added the yogurt (it was too much- I'm sure of it now) and put it in the yogurt maker. 8 hours later- watery. 12 hours later, watery. 20 hours later, watery. 24 hours later, I'm trying again. This time I'm only adding 2 tablespoons of yogurt as a starter, and I brought the milk very briefly to a boil.

We'll see.