Hey, @HeleBun
Happy to help. One things to consider when setting up weight based shipping, not only the weight of your product(s), but the weight of the default package size for your store. We have a resource on managing your default package to help you edit the dimensions/weight of this package and confirm if this is what is throwing your order weights outside of those shipping weight ranges you have setup.
If there is anything else I can help you with, please let me know.