Can I cancel it totally?
Your only way to 'cancel' it (in terms of the BTC stay where they are) is to double spend them.
Unfortunately that's not that easy. But if you have the RBF (Replace by fee) tag set (depends on the settings of electrum; it is set by default), you can simply create a second transaction spending the same outputs to one of your addresses, with a higher fee to have them 'stay at your wallet'.
However, a real 'cancellation' is not possible.
Do you explicitly want to cancel it or do you want to make it go trough ? Or doesn't it matter at all ?
Because, if you wait a few hours/days, your transaction (most probably) will go trough.