Gala won the first-leg of their round 16 tie 1-0 thanks to Mario Lemina's goal.
Gravenberch said afterwards: "If you come here you know it will be a tough game and if you play like this it’s not enough. But we know it’s only the first game, we have the second game at Anfield and we have to turn it around there.
"Sometimes we have the feeling also on the pitch that the luck is not with us. Especially in the first five or 10 minutes, I think if we scored one or two goals then it would be a different game.
"But at the end, we didn’t play a good game and we know that. Next week it has to be much better."
The Dutchman added, "If you don’t score against them and you get the first against you, with this atmosphere and with these fans it will be difficult here. Hopefully next week, we play at our home stadium and with our home fans, we are confident that we can turn it around."