the doctor who does the d and c is supposed to tell you there is always a chance that not all tissue will be removed. i mean most good doctors can get it all out, but i know each d and c i had, my doctor warned me that a second one is sometime needed.
also they are suppose to warn you about the high risk of scar tissue. did your surgeon tell you any of this? if not i would be very mad and call and make a complaint.
the dr may have screwed up. I have a miscarriage a while back and had a D&C on a Saturday, on the Monday the dr phoned and I had to see him immediately. He told me that the tissue they removed had no fetus etc so they sent me for an u/s and the fetus was still exactly where it was b4 the D&C. The dr then told me to either have another D&C or wait for it to come out naturally, so I opted for the natural way. This took weeks!. Must be so frustrating for you and I know how annoying it is when things aren't done properly. Best of luck and hope they get it right the next time!!