This well documented issue may be related to your issue (see link below)
When you try to download an area to fly in, DJI appear to limit you to a relatively small file size and therefore area. The you re-look at the area you have apparently downloaded, you will only see on the map a tiny subset of what has actually been download. I've been dealing with this issue for years but I do find that the area downloaded is much bigger than indicated. As for your "it's not showing the area I thought I was downloading" are you sure it's not just a point in the middle of (or close to) your intended flying area? To be safe I simply download multiple areas around my intend point of flight. Never had an issue doing this and always cover entire flight area.
See this also:
Using
Mavic 3 with RC Pro Controller both with latest firmware updates. Offline maps is a great addition but even though you can visibly select a slightly larger area, the actual saved area is tiny. This makes it difficult to cover larger areas you may wish to fly in. You have to download...
forum.dji.com