You shouldn’t be charged. To make sure, contact Customer Support at sketchup.com so they can help you get it sorted. This is just a forum of other users. We don’t have anything to do with billing.
You can check your plan settings in myaccount.trimble.com
There is no billing for free plans.
You will receive some additional emails during the trial period, don’t click on links to buy in them.
However, if you downloaded the ios app via Apple for SketchUp Go (for iPad),the trial of 7 days is automatically converted into a subscription.
One needs to deal with that specific plan via Apple ID settings.