In your case go to the normal checkout :)
The way around this is to reuse a light reusable plastic bag, scan the heaviest item and put it in the bag, and then put the bag in the bagging area. I never have a problem. :shrug:
It's the people who use the self service very slowly that I can't stand. The ones who don't pack as they go and only think about pack after making the transaction. They should Foff back to the normal tills for people with two left feet.