Checking your work and finalizing your curve

As you grow your curve, I recommend using the mouse scroll wheel to zoom in and out to check your work. It is often helpful to switch back to Object Mode. When selected, your entire curve will be highlighted yellow, which gives you a good reference to compare against the background image. If you'd like to evaluate your curve without distraction, you can hide the background image by clicking on the eye icon in your Properties Shelf:

Switching to Object Mode and turning off the background image is a good way to check your work