Personally I dont think its ever too late for the frog pond. I dont mind re-doing as I want what I do to really really work out. Alpaca aint cheap baby.
You dont say why you think your hat might be too big or what style you are doing. It may be possible to alter the pattern slightly - If you are knitting crown down for example (and your pattern is simple) it might be possible to just repeat rows without increasing .
You could also try rolling the brim up. Or lining the hat with a band of fleece. It will be warmer too.
You could also use a decorative pin to pinch up a bit of the brim. Pick a pretty brooch and use it to pin down a small flap of hat.
But the only way I can think to shrink the hat without felting it is to put in on a hat form (head) wet and use a hair dryer on hot. Obviously you dont want your form to be flamable or meltable. The right shape glass vase or bowl might work.
Let me know what you end up doing - post pictures!