Bad Idea? Accepted Offer BEFORE Financial Aid

[IalectoI]

I recently heard I was admitted to one of my "dream schools" and in my excitement, sent my notice that I would accept the offer of admission before seeing my financial aid package.

 

Did I make a big mistake? 

 

I've heard with undergrad, that accepting an offer prematurely can negatively impact your financial aid as it lets the school know they don't need to "compete" for you via aid.

 

However, is this the case with grad schools?

 

Just to be sure, I asked a financial aid officer at the school if accepting admission impacts the financial aid package, and she said it doesn't. However, I wonder if she was just stating the "company line," as I've also heard some friends have used admission offers at other schools to negotiate better deals. 

 

If this will indeed likely negatively impact my aid package, is there anything I can do at this point to get more aid?