I agree with sending a reminder sooner, rather than later. Also, it seems that many of my gifts were also bought at the last minute. I think people do this to help keep showers a surprise and/or to make sure their gifts are a surprise. I know I'm a last minute shopper, so I'm sure you'll see more than you expect. You will also receive lots of items not on your registry, so don't get too nervous. I'm sure it will be great.
Side note - depending on where you live, many people that were invited to my shower never received their invites due to Hurricane Sandy. If you are within that area, it may have affected whether or not some people even received their invites, in which case a call would be a great idea! It's the only way my Godmother even knew that there WAS a shower...