hi Elizabeth, noticed you were shooting in shutter priority mode also using centre weighted average so my guess is the fact that you were on an auto exposure mode the camera metered for the foreground which would be a lot darker than the sky therefore the whole image was overexposed
what you should do is expose manually also consider getting set of grad nd filters and in the case of sunset reverse grad work even better (only singh ray makes them as far as i am aware and they are expensive as hell, about to plonk cash down for one myself) to balance out sky and foreground
just remember the camera does not really know how you want to exposure the scene, learn to expose manually and when you need to exposure compensate and everything will become clear, chasing middle of the meter often will not give you the correct exposure pending on metering mode and what you are metering off
for example this shot i took few days ago
birthday sunset @Moogerah by basketballfreak6, on Flickr
i had a lee 3 stop soft grad nd (darker on the top, lighter on the bottom) to balance out foreground with light in the sky stacked with a 6 stop nd and exposed manually (came to 3 mins exposure)
especially in this case during sunset towards last light sun drops very quickly so light changes in that 3 mins so i had to actually guesstimate the exposure a bit
hope that made sense