Homemade Yogurt

A few days ago, I made my usual homemade yogurt using longevity sweetened condensed milk and the result was very disappointing. I can't really figure out what went wrong but it was too runny. Didn't look too appetizing. I have made these quite a few times and each time it turned out better. Apparently not this last time. Here's the recipe if anyone is interested:

Ingredients:

1 starter Plain yogurt (I bought mine from the vietnamese store) cup size
1 can longevity condensed milk sweetened
Boling water
milk (I use 2% because that's what i have on hand all the time)
9 big baby food jars with caps

Instructions:
Boil about 1 cup of water.
In a large mixing bowl, empty the can of condensed milk (do not discard this empty can)
Use the empty can to measure out 1 canful of boiling water and add to the mixing bowl to dissolve the milk.
Stir well til completely dissolved. Using the can, measure out two canfuls of milk and add to the mixing bowl.
Next, add the starter yogurt (stir the yogurt before adding it to the mixture). Continue to stir once it's in the bowl to make sure that it's evenly distributed.
Boil 1/2 kettle of water on the side to use as a water bath.
While waiting, ladle the yogurt into the food jars
Place the jars in a big pot and pour hot boiling water into the pot. Fill it up to about 3/4 of the height of the jars.
Place a towel over the jars and place lid over. Leave it at room temp for about 6-12hrs, then cap the jars and store in the fridge. If you want it to be more tart, let it sit out at room temp a little longer.