Air carrier Technician reported; while marshaling an ERJ 170 aircraft into position guiding it through a left turn; was not able to stop the pilots in time before the aircraft's right winglet collided with and slid under the left winglet of another aircraft.

Narrative

Aircraft X came in on a repo flight and needed marshalled into position. I marshalled the plane toward A/C Aircraft Y and stopped them approximately 15 feet from Aircraft Y. While marshalling Aircraft X through the turn to the left; I noticed after the turn had started that they had only the #1 engine running; and were moving forward more than expected. I set myself to see the right winglet of Aircraft X and the left winglet of Aircraft Y; but was not able to see the collision was imminent until it was too late to stop the pilots from continuing the turn. The right winglet of Aircraft X collided with and then slid under the left winglet of Aircraft Y. I stopped Aircraft X and contacted my supervisor and senior tech about the collision.I should have waited until more people were there to spot the winglets for me. I also should have stopped the operation when I realized that the taxiing aircraft was configured differently than I had accounted for; and would therefore be more difficult to accomplish safely.