You can always by a bag and hang it in the garage, outside, or whatever it suitable for your place.
You have any people at the gym with you that you talk to after class or friends? Have them come over and spar at home and go over techniques with them. Since this is your first time in a point sparring contest, I would try to find someone who has done it before and give you pointers.
In Isshinryu Karate, I luckily had my best friend who was 2 belts higher than me give me pointers for my first point sparring tournament since he has done many before me. One thing that I learned is that make your Kia (not sure what TKD practioners call it but the noise you make after every hit) is louder than your opponent's. It will grab the ref's attention on your strike and you will likely be called for the point.
"When I hear athletes call themselves warriors, it does bother me a little bit. When I think of a warrior, I think of the Marines I've led in combat, those Marines that sacrificed so much...no showers, little food, no contact with their family, all for their love for their brother Marine and for their love for their country. That's a warrior, willing to lay his life on the line. I've had Marines that have laid their lives on the line for the man next to him, and for their family and country. That's a warrior. The guy who goes into some athletic contest who has no war experience, in my eyes, really has no right to call himself that. That's a coveted thing to call someone, and that's what I call my Marines. Those are warriors." - Brian Stann