yep, that's the problem with swatches...they lie
As to frogging, it depends on how you want it to fit. Take the cast on and divide it by your spi of 4.25...how many inches do you get? How many is it off from what it should be for the size you want? Can you live with that? Think it will still look good etc?
You may also want to wet and block your swatch to get an idea of how much if any it will stretch to help you decide.