Garmin Drive 51 won't update

Hi

I have a Garmin Drive 51 with lifetime updates, I recently updated through Garmin Express, and it updated software, and then installed 2020.20, but only Foursquare and Parkepdia, no maps, and every time I keep trying, Garmin Express freezes, normally on 39.1% at the activation stage.
It says the update is 6.77GB, and I have a 16GB micro SD card in the device ready, but it just won't seem to get any further.
I've tried downloading to PC as well, and installing through Basecamp, or MapInstall, but they both say map won't fit and data corrupt

Any ideas please, or should I download a map from here and use that?

Thanks