Jacko,
Take a compass, when you go back, and try a change of direction, of about 45 degrees. See what you can find, if nothing, try 45 in the opposite direction. Be careful with the pozo, if you find it.
A few of them had a rock inset into the wall and after you wiggle past it you usually trip it and it will fall. Usually, not all the way down, but will block the passage and its big enough that you wont be able to move it. It will be dark as hell in there and you won't be able to see. Even if you go all the way to the end, you still won't be able to get out. I guess the upside is you would probable be rich for a little while. See if you can locate a large flat rock on top of the ground, or partly covered with dirt. Sometimes they are completely covered.