As people have already said change some up in Airport for that day .
Banks are the safest bet .
Some money changers state they are licenced but are not , used one who tried to scam me reported to police and they said no crime commited as I hadnt lost any money and anyway I had dealt with an unlicenced dealer , sign outside said licenced !!!
If you use money changers make sure that the money is in your full view all the time , have a habit of keeping money in draw on desk they say for security , count it out bring it onto desk give it to you with a smile and thank you for your custom .
Sorry to say Bali is the only place in Southeast Asia that attempts were and have made to shortchange me .
Guess what never went back .

Also insist that your money stays in view or take a photo of the money with the serial numbers easy to read or write down the serial numbers in front of the clerk so that they don't say sorry bad bill and then give you back a REAL BAD BILL which would not be the one that you gave them.