You're taking a small Westie with you as well now? How small exactly? No wonder you're in a panic!
Personally, I'd speak to the ferry driver the night before, and offer him a decent tip if he'll give you a lift back early the next morning. I'd imagine that's a common request, and you might not be the only one.
I think your only other option (unless the River Falloch is running low enough to wade over) is to walk two miles along the A82 until the bridge at Beinglas Farm Campsite, where you will be able to rejoin the proper route.
HTH!