Goals from Atsuto Uchida, Kevin-Prince Boateng and Julian Draxler after the break were enough to secure a win for the German side in their UEFA Champions League opener, much to the frustration of Steaua, who created a flurry of chances in the early stages of the second half.
Steaua were making their first appearance in the Champions League since 2009 and Reghecampf insists his side must improve if they are to make progress.
He said: "We have to learn from these mistakes. They scored at their first goal opportunity.
"This happens in football when you make childish mistakes. We can beat Schalke in Bucharest."
The result leaves the Romanian side bottom of Group E on goal difference, ahead of a home game against Chelsea next week.
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