The final preview (unless you have endsheets or inside printing) is your full cover with bleed.
Red dotted lines represent the "Trim Line" for the cover. This is where your cover will be trimmed, the outside area will "bleed" the cover content to the edge of the cover, and will most likely be trimmed off.
Blue dotted line represents the center line of the cover. Everything to the right of the center represents the front cover of your yearbook.
Tip: If you have text on the spine of your cover, make sure that the text reads from left to right, top to bottom.
Once you are happy with your design, approve your cover by scrolling down to the bottom of the screen and filling out your information then hitting "Approve Cover".