She answered why right above your post.
Turbo Tax starts out by giving you the full Stimulus amounts and then later you enter what you actually got for each one. So you only get the difference if you qualify for more. You are not paying tax on them. But Turbo Tax started out by giving you credit for the whole amount so you refund was too high. Then when you entered what you already got the starting refund was reduced or the tax due increased. You don't get it twice.
