Paula - kudos to you for sticking to your exercise plans!
The only two RB exercises that I know that don't involve standing (like squats and lunges) are leg press and leg lifts.
For leg press, you lie down, loop the band around your hands a few times until it's short enough, place under the center of your foot, and press up at a 45 degree angle (kind of like a lying 45 degree leg press).
For leg lifts, you put the band under the center of your foot and do straight leg lifts. It's harder to do both feet at once, so do one at a time if both are too tough.
How about sitting down abductor and adductors (inner and outer thighs)? I've only done these standing but what if you tried in a chair? (heck, may as well try, right?!) Make a loop in the RB and put it around your ankle. Stick the other RB handle around a sturdy piece of furniture, like your dining room table or the leg to a sofa. Sit in a chair and press away for outer thighs and turn the other way and press across your body for inners. Here's
a little video with the general idea.
Do you have ankle weights? (the kind that velcro around your ankles) You can do leg lifts, side leg lifts, and butt kicks with them - just start on your back, do leg lifts, roll to one side and do side lifts, on your stomach for butt kicks, and other side for side lifts. Then do the other leg.
Good luck! I'll bet you'll get some other good ideas.