I made my own sugar syrup (2 cubs sugar into one cup boiling water.)

I want to know if I can store it in a simple cabinet or is it best to
store it in the fridge? My tropical drink book says to just store it in the
dark in a cupboard. But when I look up sugar syrup on the net many sites
say to store it in the fridge. Does it mater where I store it?

Also, I put my syrup in a used Diet Coke bottle that I washed out a few
times. Is this ok?

Thanks