Im not an expert on these type of things but i am in the home construction industrie.
Have you considered on calling back the contractor that built the home and ask why this was missed?
I know when we build our Basements after the walls a placed in we do what is called a restone around the footing of the foundation and call in a backfill inspection and fill in. The excavators are responsible to fill in the hole and from what it sounds to me that they didnt leave enough dirt behind. You might be able to get your contractor to call them back and fill it in properly for free. Ive seen it happen from time to time. its not really the builder fault, im sure the excavators had a long day or whatever the situation was at the time and just filled in what was there.
I certainly hope that it isnt a seriouse slop to your home for i fear there was a mistake in grade/elevation of the home in general.