Q: "Am I doing this workout wrong if I'm feeling it more in my hip flexors than in my abs?"
Nothing wrong with working your hip flexors. Your hip flexors (muscles of the deep lower back and upper thighs) might be the most underdeveloped muscles in your body. This is likely so for many reasons.
1 - We sit all day long. Sitting puts the hip flexors on slack. When a muscle is put on slack for long periods of time, day after day, it loses strength and range of motion. Weak, shortened hip flexors are probably the number 1 contributor to low back pain. It is a condition suffered by an estimated 80% of us.
2 - It's not easy to work hip flexors. There aren't many natural positions outside of situps and leg raises that work the flexors of the hips. Tons that extend the hips (squats, running, dead lifts, etc.). But not many that flex the hips. So, most folks skip working them due to lack of knowledge and experience with these movements.
3 - Hip flexors aren't comfortable to work. Somehow we have all gotten used to the deep muscular burn felt in our legs, back, chest, shoulders, bis, tris & abs when we work them. We've even come to like it a little. But, the deep ache we feel in our low backs and around the tops of our legs when doing hip flexor work is unsettling. Most of us associate it too closely with injury. So, we fear it.
4 - Fitness experts in the 90s told us to quit using our hip flexors. Back then, exercising was all about isolation and development. Real body building stuff. Those who were trying to build abdominal bulges (usually compensating for a lack of bulge elsewhere) would try to eliminate all muscle groups in a movement not associated with said bulges. This mentality is still (wrongly) with us today.
Keep in mind, just because you aren't feeling it in your abs, doesn't mean your abs aren't getting all the health benefits of the workout.
Another thing to keep in mind is you MAY NOT BE ABLE to work an intended muscle (abs here) if the supporting musculature is weak. We've learned that the place you feel a compound movement (a movement involving multiple joints and muscle groups) is usually the weak link in the chain. It will be hard to feel the abs working until the hip flexors come up to speed, in terms of strength and endurance. This MANDATES hip flexor work.
Hip flexor work is extremely important to Optimal Health. Remember, over developing certain muscle groups brings with it all of the negative health concerns as under developement does. Those who work the hip extention (squats, DLs etc.) without considering deliberate work for the flexors are in for a world of hurt.