Why does pip go alone to the sluicehouse in the marshes in the book Great Expectations?

Answer 1

He goes alone because the anonymous letter demands that he go alone to the little sluice-house by the limekiln on the marshes; he is afraid to disobey it, for fear of endangering Provis/Magwitch even more.

Answer 2

Pip goes alone to the sluicehouse in the marshes because he believes he is meeting the escaped convict, Magwitch, without notifying others. He feels a sense of duty towards Magwitch, as the convict had asked him to bring food and a file. Pip also doesn't want to involve anyone else in potentially dangerous or criminal activities.