My bed currently has some spots where there was najasat. At this time I am unable to clean it properly. If my bed is dry. Can I sleep on it?

Cleaning it is not mandatory.
You can sleep on it, as long it is dry, and your body is dry.
If your body got wet, and contacted the najis area, then you need to clean the area that got in contact only.
You can put a sheet on the unclean area.