Payroll error in my favor question

So I noticed on my paycheck Friday that I was grossly overpaid(like it was twice the amount). I did the right thing and reported it this am to payroll. I am waiting to hear back from them about how they are gonna reclaim their money back(they are gone for the day but mentioned taking it back the next two paychecks when I briefly spoke with them this am). Here is my question...because my check was such a large check, they took out much more in taxes and retirement(obviously). So, if they were to take back the total gross amount, it basically leaves me as if I was only paid $500 Friday. Can they take back the gross amount...even though I already paid taxes on it?

I'm stressing out cause I'm beginning to feel that I'm gonna get screwed for doing the right thing. Any of you money masters of the OT have any experience with this?