I'm not sure about the mistake @.@
When the silkworm gets through to lay its eggs, it dies.
The mistake in this sentence is "to lay"

So I correct to "laying" because it stands after "through", a preposition

Question

I'm not sure about the mistake @.@
When the silkworm gets through to lay its eggs, it dies.
The mistake in this sentence is "to lay"

So I correct to "laying" because it stands after "through", a preposition

Answer

Your answer is correct, but the methodology is not. The phrasal verb "gets through" requires a gerund as it object, hence "laying" instead of "to lay". The phrase "gets through" is the same as "finishes".