No need to undo it if you planned on keeping personal files in it. mkdosfs is pretty much the same as a DOS format c:, it just leaves you with an empty fat partition.

But I dunno exactly what you have been doing with your memory card, honestly after so much meddling you have to check. How big is the fat partition in it? Is it the full 2gb? Or are there other partitions there?

might help clarify things. If it only shows the one partition for /dev/mmcblk1 (your /dev/mmcblk1p1 that is) then you just have 2gb of free vfat memory =). If not you can run sfdisk on it again and partition it as you wish.

Just checking, do you own an N800 or an N810?