This came from a little car, and I'm trying to build that car using LDD, but I can't find the piece. Can someone help?
On Bricklink this is called Wedge 3 x 4 x 2/3 Cutout.
As Uli pointed out in the comments this part is called "FRONT 4X3X2/3 W. BOW" in LDD. The given image looks very similar. You can also see if this is really the part you're looking for by looking at the 3D model of it.
How I found it: Searching by properties did not work (which usually does), and I knew that many Lego city police sets had red-colored vehicles, so on google I searched "lego city police" and hit images, and I saw an image of the front of the box for set 60243 which showed a truck that seemingly looked like it had this piece and I found the same set on bricklink. Then I looked at the part list, and it had this part!