The Dutch manager was disappointed with the profligacy of his side but is still optimistic of progressing to the knockout stages of Europe's premier club competition
The German side were leading 2-1 with only seconds to spare before Souleymane Camara snatched a late equaliser for la Paillade, who had been reduced to ten men.
There was further bad news for the Gelsenkirchen side after it was confirmed that stand-out performer Julian Draxler requires surgery for a broken arm.
The 19-year-old scored his side's first goal before being injured when winning a penalty for the second score, a move which saw Garry Bocaly receive a red card.
Speaking in his post-match conference, the 58-year-old coach said: "Yes, he [Draxler] broke his arm and he will have surgery tonight.
"Of course we are upset. They have two shots on goal and both of them go in."
"We needed to clinch this game earlier. Even against ten men we should know that at Champions League level you need to make the most of your chances."
However, despite surrendering the lead late on Stevens believes that his side are in a good position after their opening two matches.
"In the last minute we conceded from a counterattack, despite having a lot of opportunities before that. We just need to be more efficient," he explained.
"You could say that we dropped two points today, but then we also have four points under our belt already and we just need to keep going strong – it's as simple as that."
Schalke sit in second place in Group B and travel to the Emirates Stadium on Wednesday, October 24 to face leaders Arsenal.