Use the wand and bucket to fill in the other large areas until your image looks like this:
The gaps in the outline are now more easily seen. To replace them, use the paint brush with black as the color. Set the brush width to 1 or 2 pixels. Be sure to select the entire image using 'Edit' and 'Select all' from the drop down menu. Now just click on the image where the missing pixels should be.
All that is left to complete the silhouette is to paint in the bottom area. Make sure you have the entire image selected. To thicken the bottom in order to make it easier to 'stay in the lines' just use the 'Line Tool' with a brush width of about 4 and black for the color. Draw a straight line across the bottom and the use a wider brush to paint in the rest of the teapot.