But i sent it 6h ago so it should be done already, right?
I am guessing that you submitted the transaction from an exchange 6 hours ago and it was only actually added to the Eth queue 20 minutes ago (that's what the explorer indicates). The exchange might be bogged down and only just submitted it. You should expect it to take another ~4 to 6 hours before it processes if the calculator I cited is accurate.
As long as you sent it to the correct address, I wouldn't sweat it. The transaction is not going to disappear, it will just take a while due to the low gas price.
It looks like you can resubmit the transaction with a higher gas price that should solve your problem. I have not looked at it carefully but this may be helpful
https://www.reddit.com/r/EtherDelta/comments/72tctz/guide_how_to_cancel_a_pending_transaction/.
If you do resubmit with a higher gas price, try using like 80 Gwei so it is transacted very quickly!
The process to override the gas price with a higher one seems very straight forward after reading over it. I suggest you carefully follow those directions with a Gwei price of 80 that will allow it to complete in ~30 seconds. Be careful to use the right web page (avoid phishing), and to set the gas limit amply high (having the gas limit too low can get the transaction thrown out. 210000 like you did should guarantee it processes I THINK, but you may want to check).
If you're freaking out right now, maybe come back and do it later when you're calm so you don't make any mistakes. Good luck!