planted SOME POTATOES IN A BAG

do you mean a bag they came in or a grow bag ?

I planted them in a large canvs bag. They just seem to be so tall I wonder if they are all foliage, and just producing flowers

I've never heard of a canvas grow bag...

And that comment didn't really answer your question potatoes do grow tall. did you put the tubers well down in this bag and then keep adding more soil/compost as they grew? Or did you almost fill the bag with compost and just put the potatoes into it? Either way you will still, or should, get potatoes.