@Priscilla ,
You will have to set up a ‘grid’ type mission similar to this image and take multiple photos, each photo overlapping. You can set individual waypoints to capture the images, or you can set a photo interval (seconds or feet) and capture them
Those photos will have to be stitched together to form a large orthomosaic image.
Litchi can certainly handle the image capture, but it will not stitch the images together.
You can take a look at this topic.
Good luck.