Hey MM, don't get discouraged. I had a hell of a time with the air bikes the first week and couldn't really do them right but by week 10 I was laughing at myself for thinking 12 was nearly impossible- thats how easy they had become in that short time.
Kristin suggestion about putting your hand on your abs to focus on them. Slow is ok- its actually better.
Some Physical therapy exercises I was doing to help ( add 10-15 of these in every day if you want)!
Pelvic tilts-- there are many variations of these, like lifting one knee, swimming arms up, balancing on a foam roller while doing them.
They are all low impact, but excellent way to increase ab strength without pain.
I don't think you need to worry that your abs aren't getting worked enough because they aren't sore. I didnt have too many days where my abs were sore.
You're doing GREAT! Keep it up!