Select the newly detached hood and right-click on it and select "Hide Selection." This will remove it from view since we don't need it right now.
Select the edges around the hole of the hood and extrude them inwards a little to create a lip for the hood area. Chamfer the edges by the same amount that you chamfered the headlight area to make the edge sharp.
Perform any vertex cleanup that is required. When smoothed, the car should now look like the picture.
Now you need to unhide the hood from earlier. Right-click in the viewport and select "Unhide All" from the menu. Select the body of the car and right-click and select "Hide Selection." This will leave just the hood visible.
Select the edges shown in green and extrude them downwards a little to create a lip on the hood. Select the same edges again and chamfer them by the same amount that you chamfered the around the hood on the body of the car. Add a Symmetry and a MeshSmooth modifier to the hood. If you have done everything right, the hood should fit in the car perfectly.
Once again, if you smooth everything, you should have a nice seam around the hood like what is shown in the picture.
Next we are going to add a lip to the bottom of the car. We are going to do pretty much the same thing we did for the hood. Select the edges around the front wheel arch all the way back to the rear wheel arch as shown and extrude them inwards a little. Make sure you only extrude inwards a very small amount. Do the same for all the remaining edges around the bottom of the car. Chamfering is not necessary in this case.
Time to work on the trunk area in the same way that we worked on the hood. Cut in some edges on the back as shown by the green lines. Then select the polygons shown in blue and detach them from the mesh as you did the hood. Select the detached trunk polys and hide them to get them out of the way. Now back on the body of the car, select the red egdes as shown and extrude them inwards a little to create a lip for the trunk. Chamfer the edges as you did before. Now unhide the hood and do the same. If you don't remember how, just go back to the hood section and and follow the same steps. Make sure to tweak things to your liking.
If you did it right, the trunk should look something like the picture.
You will notice that the trunk has a grill on it because the engine of this car is in the back, not the front like most cars. The next step is to make the hole for the grill. We are going to use a new tool called "Inset" to do this. Select the polys shown in red and then click the little button shown next to the button labeled "Inset." The "Inset Polygons" dialog box will appear. For the inset amount, I used a vaue of 10 but it's not really important.