Dear Lonely Hufflepuff,
The way I see it, having 2 or 3 close friends is better than having a lot of acquaintances or no friends at all. If you value the few friends you have and you know they value you, then don't worry about having a whole bunch of additional friends.
When I was in school I didn't have many friends either. But the ones I had were worth more to me than anything. Just be yourself, and don't try to impress anyone. People who are worth it will appreciate your kindness. Anyway, you still have 5 years of Hogwarts to make more friends! Join a few clubs or try out for Quidditch! You may meet people with the same interests as you.
If all else fails you could always make friends with the centaurs in the forest. All of the creatures are quite nice, actually. Although, I don't think I'm supposed to encourage anyone to go against the rules and visit the forest...Oops!
Good luck with 3rd year! Have some pumpkin juice at the feast for me!