You received this warning with your Online PDF proof if you haven't applied the bleed correctly.
Bleed is used to avoid strips of (white) paper showing on the edges of your print should the batch be misaligned when cut to size.
Jukebox Print recommends bleed of 0.125 inches on all four sides of the page - if you have less bleed, you might see strips of paper showing on the edges on a portion of your order.
You may proceed with printing your Online PDF proof as is by clicking Approve Proof, however, we recommend uploading a new file with full bleed.