Sorry for the late response. If it's still downloading after this long, then it is a problem. I'd try to do a soft reset on your device and try to download again. Just don't ever do a reset while it's trying to actually install.
Most likely it isn't a problem. Just make sure your signal is good for the method of download, whether that be Cellular or Wi-Fi. It can take a while to do the download, and the progress bar frequently lies.