Hello Mona,
I have the same issue. Still, I wrote to the hotel today hoping that if someone cancels they will contact me. Let's see how that works for me.
In the meantime, I've a booked a room in a hotel nearby: Hotel Potsdamer Hof Berlin. I chose this hotel for it's price and proximity. I can still cancel my booking by the 4th of May.
If you can't find a roommate or you don't like your options I can try to ask for a twin room in this hotel and we can share the room.
I will be traveling from Belgium and wouldn't mind some company.
Good luck,
Silvia