"was" is indeed a short form of "etwas" = something.

"wieder holen" is not the same word as "wiederholen" (=to repeat). It means to retrieve (fetch again).

"lan" is short for "lassen" (=to let). Again guessing, it may be from the Swabian dialect.

An interesting text, quite unlike German trad song I'm familiar with. In its form it is more akin to a Child ballad - I wonder if it's a derivation from a British trad song.