Not really clear. You mixed the 5oz priming sugar with water for simple syrup, then divided that into thirds using 1/3 for each batch? If so, you're fine
We definitely need some clarification. If you did what was said above, then you're fine. I'm reading this a bit differently, though.
To me, it sounds like you made a syrup using the 5oz of sugar, then used a priming calculator to determine how many ounces of sugar to add. At that point, you added that many ounces of syrup rather than that many ounces of dry sugar to each batch.
If that's the case, then I think you should just make do with slightly undercarbonated beer. First of all, it will be tough to determine exactly how much sugar made it into each beer without knowing the exact concentration of the final syrup. Second, 5oz of sugar is almost always too much for a typical 5-gallon batch. You will probably end up with a beer that is carbonated on the low side, but not undrinkably flat. Rather than mucking around with how many milligrams of sugar to dose in each bottle (which is do-able, but not worth the effort), just chalk it up as a learning lesson and drink it as-is.