From my own end i will say cash out this time around is difficult, maybe I will say it is because of the just concluded international break.
There is one unfortunate circumstances I will never think of forgetting some times ago when Manchester united played against arsenal after winning Manchester City, in that game I staked Manchester united to win. After that first half equalizer and a lead in the second half, the game was in good condition until arsenal equalised, out of fear i cashed the game out without knowing that in some minutes' time united will surprised all and it was a thing of regret at last.
You really over estimated Manchester United and you feel that man United is that consistent enough to win on multiple legs game because at some point, Arsenal can not be equated with Manchester United no matter which club Manchester United may have beaten at any time, so you should have cashed out the bet in the 1st half of the game, since you where in winning through 1st half of the game.