If I understand correctly, I now have to create a new transaction from Electrum. I enter the same address in 'pay to' and the same amount. Then send the transaction and broadcast it? Is that all?
No. Double spending requires that you use the same inputs... If you just create a new transaction without knowing what you're doing, you could spend "different" coins and end up sending 2 payments! Best wait for mocacinno to help! 
Good thing I have not taken action yet, cheers for the heads up!
I don't know then what the same inputs means, I thought it would be the address and amount you 'put in', but I'm just a scrub.