As the forum overall tends to be used primarily by independent travellers vs. a package tourist it is true to say that there is often an anti-tour bias to comments. Bus tours of 12 cities in 10 countries in 14 days will usually get negative comments. Tours that are known for drinking more than anything else (Contiki et al) will also get negative comments.
So I would say the OP is right in her observation batty.
Originally, the OP wrote that she was travelling alone. Later she clarified that she was travelling as part of a Top Deck Tour. So not alone at all in my opinion. Interesting that she thinks she is travelling alone.
So she is taking a tour of X number of places by bus in Y number of days. Her big issue is whether within that group of 20-30 people, to share a room with 3 others or with only 1 other female. I think JimBurns got it right in #17.
Alazabel, consider this your first anti-tour comment if you wish, although I think there would be more by now if people had realized you were in fact talking about a tour, not about going to hostels independently and asking about whether to book a dorm room or private room. That is in fact what most answers have obviously assumed. ie. why else would people be telling you you have to pay for 2 beds; why would I have wrote about not booking ahead; etc..
Please tell us how many places (and which) you will visit in how many days. That is what most object to about tours like this. Trying to see too much in too little time.