I want to make a makeshift curtain for around my bed?

I have to share a room with my sister and it is really annoying because she is always bugging me and always leaves the lights on at night. Im on the top bunk of a bunkbed and i want to make a curtain using bedsheets or whatever to block out light and make it my own space. I tried using ropes and a packet of blue tack but i cant get it to stay up. Any ideas?