You just 'saved' it and wasn't broadcast yet to the network.
You can safely delete it from the history by doing right-click->delete (do not right click to the label) and your previous balance should return.
This is correct.
However, there might be an underlying problem with your connection that caused this issue... So you can safely remove the old transaction, but if you create a new transaction you might run into the same problem if you don't fix your connection...
Is the button on the bottom right of the electrum window green?