my first yeast starter trial

I follow procedure of whitelabs.

I use cooking pot to mix DME with heated water and boil, to prevent over boiling and foam eruption. And I don't need to use fermcap

My case for trial:

Aim for 1.037 initial gravity 

51g DME

500g water 

0.5g yeast

0.1g yeast nutrients (optional)

Turns out result in SG of 1.04

Measure with hydrometer, it's 1.040 to 1.042

NB: I only boil wort for 3 to 5 minutes instead of 10 min. Will this not enough time for amylase to convert starch to sugars?

After 12 hours, foaming:

After 24 hours: foam reduced

Let's see after 48 hours.

When to add yeast nutrients