529 plan accidental withdrawal - tax and penalty implication

I talked to my son's 529 plan administrator about the recent withdrawal, and she told me that when I deposit the exact withdrawal amount back to my son's 529 plan (no time restriction), I will not incur any tax or penalty.  She told me that when I will get 1099-Q and I just have to say that I didn't use the money and put it right back.  I told her that I will be withdrawing the correct amount for my son's college tuition later in the year and she told me that won't have any impact.  I just want to check to see if it is really this simple that I have to do is just depositing the same amount back and there will be no tax or penalty.  I read online that depositing the amount back will be treated as new contribution and will incur tax and penalty, but the 529 plan administrator told me they are the experts dealing with 529 plan and to talk to them directly instead of reading misinformation online.