Kingsley Coman struck the only goal of the game at the Parc Des Princes as Bayern Munich took a slender advantage into the return leg in Germany.
Mbappe was only fit enough for a place on the bench after making a quicker-than-expected recovery from a thigh injury.
His appearance off the bench reinvigorated the PSG attack but Mbappe had a goal ruled out by VAR for a marginal offside decision.
PSG have it all to do at the Allianz Arena but Mbappe believes qualification to the next stage is still in sight.
"As we said, we said we had to take the positives. It's a two-legged tie. We can't change what happened in the first leg," Mbappe said in quotes reported by PSG's official website.
"We will go there to qualify. We know that there is a possibility. There is always a good possibility to qualify. So we will go there with a lot of energy and determination.
"It's not a comeback. There's no longer the away goal. We have to score a goal and we'll be level, so we have to go there and win.
"Play our game, play attacking football, which we know how to do and try to go there and win."
"I wasn't supposed to play but I wanted to play and help my team-mates," he added.
"We did everything, we worked night and day to get me some game time.
"I wanted to [start the game]. But sometimes you have to be satisfied with what you can do, and that's all I could do.
"My feeling? I was a bit concerned, but I gave everything I had and I have nothing left. Now we have to continue and recover well.
"Like I said, get everyone back healthy and all come back at 100 per cent, and I'm sure it can go well."
