I don’t know how you found that store, specifically, but Prague powder #1 is 6.25% nitrite. It’s a proprietary blending. What I read there was most likely a misprint. Either way you are still fine.
I would suggest in the future, to source the cure #1 from The Sausage Maker, or from Butcher Packer. There you also find plenty of other needful things. The Butchers Pantry is another source.
With the high salt concentration of your brine, I think I would pull the meat at 8 days. You are working with pretty high salt concentration for palatability. Plus the high salt speeds up the curing process.
Next time do an EQ dry brine (what I do) or the EQ wet brine, you will enjoy the next one much more. This one will be fine, but salty. You are in the learning curve. We have all been there. It gets much easier and better the more you do this.