The idea of "flat abs" is brilliant marketing, because it's not realistic for most people. That said, if you have a disproportionate amount of fat around the waistline, this can be a risk factor for diabetes, metabolic syndrome, PCOS and more.
No amount of planks or pilates will compensate if you are not eating well - that doesn't mean restriction and dieting (nasty cycle that will only make you feel awful!) but that you are aware of eating a decent serve of veggies (especially green), fruit (so many choices!), legumes, wholegrain carbs (love rye bread or wholegrain pasta) and lean protein (fish, skinless chicken, prawns, tofu).
This time of year it's tempting to overdo everything but try to keep your workout routine. Not just for the sake of your abs, but your sanity.