Should I get a d and c if I had a miscarriage on week 3?

Depends. If your miscarriage results in complete passing of the pregnancy tissue, a D&C may not be necessary. If the tissue does not completely evacuate the uterus, your doctor may recommend a D&C to avoid future complications such as infection, excessive bleeding, or other complications.
No. Most woman who have a miscarriage in the early first trimester will be able to miscarry without the need for a d&c. If however, the woman has prolonged, heavy bleeding, this could be a sign of an incomplete miscarriage and requires medical followup.