Yes, you've tried it correctly but that's sadly due to the current high ethereum fee 
https://ethgasstation.info/
All transactions currently are quiet expensive, I hope that there'll be some better time!
if indeed you intend to make an airdrop it means you also have to be prepared with gas, if we have to pay for gas it means not an airdrophttps://ethgasstation.info/
All transactions currently are quiet expensive, I hope that there'll be some better time!
Airdrop is free and doesn't cost anything