"Gaping hole" is a bit strong. It basically worked, it just wasn't the smoothest learning curve.
Now that you've explained it, I totally get how this room was supposed to work. If I had actually held down J, it would have done a really good job. What actually happened when I played it was:
1) The first time I tried to drill, I must have been jumping. This caused me to shoot up into the ceiling and die.
2) Since I didn't want that to happen again, I made sure not to hold down the drill key, meaning I got stuck in the middle room. It wasn't until I worked out downward drilling that I was able to get past this room.
It's tricky to teach this mechanic without straight up telling the player what to do, but I think the game is better for it. Maybe if the ceiling on the left were really low, so the player could only enter the wall at ground level?
Btw, I feel like you're being a lot harder than yourself than you need to be. This is a genuinely good game, especially given your time constraints.