On Sunday the 14th it became very cold, we could not stay out on deck, so we all came together in the dining room for a hymn sing, finished up by singing, “O hear us when we cry to Thee, for those in peril on the sea.” Little dreaming(?) of our own peril soon to be.

This is right, but "little dreaming", is a clause connected to what comes before. She means "not aware" or "unable to imagine".

I heard a loud scraping(?) noise.

Correct.

The great ship (?) and stopped.

The great ship shivered and stopped.

We had been going 28 knotts an hour, the sudden silence seemed strange and yet the impact was so slight(?) the three girls slept through it.

Correct.

...but(?) we must go to the boats(?) + get off, to lighten(?) the ship so the water tight doors could be closed.

I think that's right too. Not sure exactly why lightening the ship would do this, but that's what she wrote.

...neither the boatmen or the passengers had had any boatdrill(?) and yet there was no panic...

Correct.

but only 20 lifeboats each (?) for 65 (?)

But only 20 lifeboats, each built for 65 persons.