Did it say what kind of jars to use? The standard Ball canning jars are smaller than what it looks like you might have been using. It is possible that at those sizes it would have filled 8. Who knows though. It looks tasty! My mom used to make strawberry jam and I would eat it all the time. That does seem like a lot of sugar! That is the cool thing about making it yourself, you can adjust those quantities unlike the stuff you buy at the store.