Is Told us you needed three books complete sentence?

Told us you needed three books is not a complete sentence. It lacks a subject.

For example, adding I, she, he, a person's name or a title would make this a complete sentence.

Examples:

He told us you needed three books.

She told us you needed three books.

Mrs. Krammer told us you needed three books.

The teacher told us you needed three books.