What type of stakes are you using? Last year (my first), I had 2' wood stakes with 18" high OSB and I drilled through the mending plates into the stakes. The stakes were almost 2" thick, so a 2" screw worked for me.
This year, I got lazy and decided against mending plates in favor of just overlapping the OSB a few inches at the junctions, and putting a stake on either side. Still drilling directly into the stake from the inside of the OSB, but now I don't have to line it up just right. We'll see how that works out, as I haven't filled yet :)