Look how far you're going.

I spoke to a woman whose company had recently been investigated.

Perfect — whose neatly combines the two sentences into one.

If I were you, I would start a new company.

Correct — great use of Type 2 conditional with "were" (not "was") for hypothetical situations!

The mosque saved me from bad friendships.

A beautiful, natural sentence — correct exactly as you said it.

I felt like an angel.

Beautiful, natural sentence — keep saying things like this.

He claims that we refused to open the file.

Great use of claim + that — to say something is true without proof.

If I had 8 days in a week, I would work more.

Correct — great use of the Type 2 conditional for a hypothetical situation!

He is less likely to leave the country after the liberation.

Excellent — perfect use of less likely to + verb.

He was the doctor who gave her the anesthetic.

Nice — correct relative pronoun who for a person.