Contribution Withdrawal from Roth IRA - Question

I want to pull some money out of a Roth IRA I have set up that will be less than the total amount contributed. I called vanguard and they said it's as easy as giving them the OK and they'll send the money. He said the burden is on me to prove to the IRS that i withdrew less than i've contributed using various tax forms available from their website showing my contributions and withdrawals. is it that simple or is there a catch somewhere that i might not be seeing? i don't want to put myself in a bind with extra taxes and penalties.