about 2 months ago - SylenThunder - Direct link
Since the changes to the way ore deposits are on the surface, I rarely find a need to dig deeper than about 20 blocks when mining. Usually by eight blocks down you are into the stone layer and the ore is spread out to the sides. Makes it pretty easy to build a staircase exit.

OP's issue sounds like they aren't able to place a block, which could be a sign of corrupted stability calculations. This happens a lot with large underground excavations, especially if a lot of bedrock was exposed.

Attempting to flatten the area isn't going to do much of anything. Sounds like you dug rather helter-skelter to where you are. You should be able to dig an upward slope to get out, or re-connect to your already existing tunnel if you can map it's location out.