Serhou Guirassy was happy to finally make his debut for Borussia Dortmund on Friday evening against Heidenheim, but still sees room for improvement. “I can’t be 100% yet. For that I need more games,” he said after the 4-2 Bundesliga win. The summer signing from VfB Stuttgart missed the first two Bundesliga matches due to a knee injury. “First of all I need to remember the basics. Three months without a game is a long time,” he said. Guirassy didn’t score against Heidenheim, but was praised by coach Nuri Sahin, who described him as a “fantastic football player.” Dortmund sporting director Sebas…