So OP acknowledged

A. The wager was placed with reliable knowledge the game would not be completed due to weather

B. Not being aware of the rules and assuming because the game is played one way one place..no need to assume its different anywhere else.

Sorry, but if they voided- they were right in doing so. You acknowledge not reading the rules before..and placing the wager in anticipation of a shortened game.

Why not play a 5 inning line if bullpen/short game was a concern? What advantage did you see in a rain shortened game (assuming you didnt bet a spread/Runline, where the advantage is clear).