I'm hoping mine will get that big. Right now they are 2nd instar and about the size of an ant... But I will do what you suggest and hopefully the other two will make it. Yours is a little beauty already!
They are quite hardy little critters, and rarely are losses incurred.
I say this not to make you feel bad about the one you lost, but to give you confidence about the 2 you have left. No need to dote on them either. Just keep them a bit moist.