I think marco has a good point, you should definitely not lose money at this point. I haven't seen first game or two predicted pitchers, but my guess is Boston will be favored at home.
Maybe consider dividing the hedge up a little. Place $100-200 on Stl to win series, if Boston wins game one or games one and two at that point place another 100-200 on stl in series, number would now be +300 to +400 range, now you have locked up a sure win it is just a metter of how much.
Stl is tough at home, if they can get a split in Boston all of a sudden your series bet doesn't look as good.
Hope it helps.