But the defender believes his side can kill the tie off by adding to their goal tally at Villa Park in two weeks' time.
McArdle headed Bradford's second goal last night as they followed up the Premier League scalps of Wigan and Arsenal with another outstanding performance.
It was enough for many bookies to make the League two side favourites to reach Wembley, but McArdle told talkSPORT: "They're still probably favourites in footballing terms but all the pressure will be on them, we can go down and enjoy the day.
"We know we can create chances and if we can nick a goal down there it makes their task even bigger.
"If you go down with a defensive set-up, you invite pressure. We know they'll have spells where they get the ball so it's important we get up the field and get the ball in the box."
With defensive colleague Carl McHugh also on the scoresheet and goalkeeper Matt Duke again earning plaudits with a string of saves, McArdle savoured a fine team effort.
"We know we can always score goals and last night me and Carl both managed to get a goal to take the pressure off the boys who've been doing well in front of us," he said.
"We passed the ball great, especially switching it through the midfield, but we know if that's not working we've got a good aerial threat and the delivery was great from (Gary Jones).
"I thought we deserved the win, we created chances. They had chances as well but Dukey was in fine form, as he always is, and kept us in it.
"He seems to be doing it more often than not, especially in the cup, he's had some magnificent games."