That’s because you have an onSubmit action that Adds a Row.
So when your form is submitted, a row is added. And then your onSubmit action adds a second row.
You need to get rid of that onSubmit action.
I’d also encourage you to have a closer look at what @ThinhDinh said earlier…
The above is a much better approach than messing around with GSheet formulas. As a general rule, you don’t need any GSheet formulas when working with Glide (except in very rare cases). The Glide Data Editor has all the capability that you’re ever likely to need, and your App will perform much better if you avoid GSheet formulas.