Did you check if the drill bit was slipping in the bushing or if the whole jig was flexing when you clamped it down? Those cheap dowel jigs can work but you gotta clamp them tight and go slow, and even then the bushings wear out fast and start wallowing out the holes. Honestly for face frames I gave up on dowels and went back to biscuits with a good fence, way more forgiving and faster for me. If you really want dowels, the self centering ones from Milescraft or the Jessem are night and day better than the HF one. 16th off is brutal though, that's enough to throw your whole frame out of square so I'd return it and put that 85 toward something that holds its setting.

My grandpa had this old trick with a length of chain and a strong magnet, he'd drop the chain down the wall cavity from the attic and then drag a magnet along the surface to snag it. Worked like a charm on lath and plaster because the chain doesn't care how thick the wall is, it just needs to find the magnet through the gap. I tried it once on a 1920s bungalow and it took maybe 20 minutes but zero holes, which beats patching plaster any day. The chain has to be small enough to slide down but heavy enough to swing toward the magnet when you drag it. He used brass chain off an old lamp pull, and I still have it in my bucket. The learning curve is real though, you'll cuss a few times before you get the feel for it.