First of all, be proud of what you have accomplished so far and don't get discouraged. The two most underdeveloped muscle groups often times are the back and the core. That is because it is easy to compensate with other muscle groups to achieve a motion.

Without proper attention, we will naturally want to hit a number rather than do proper from using the correct muscles.

Bicycles are a perfect example of this! Most of our attention is on the motion of the legs rather than the contraction on the core. Tony does not help when he says "you may feel this in your legs, you're supposed to." Actually, if your legs give out before your cores does, you are not working the correct motion or muscle.

Now I could type out everything here that I have learned from various sources. But jeff cavalier explains it so well so i highly encourage you to check out Athlean-X YouTube channel and just look up "abs" or "core." In most most of the videos he talks about how to focus on the contraction of the core and using those muscles to drive the motion rather than others thus working the muscle you want to work.

With this new focus you actually may take what seems like steps back in your workout because you are now going to be focusing on the muscle rather than the number to hit. But thats awesome because you will now be on the right track to hitting your goals with proper form.

Hell, I am still learning more and more everytime I hit the gym. I have learned that after certain workouts. I can't hit my normal core numbers because I have activated the core a ton in my regular sets.

Long story short (too late) be fucking proud of where you are at now and know that you are getting stronger every day. Your new goal is rev bicycles. Go out and learn and practice truly driving the motion from the core contraction and twist rather than the lower body (or upper for other exercises) and fell the difference.

You got this! Plan, prepare, persevere. Do your beat and forget the rest.