HEEEEY Surfie surf! I went out with a surfer, and surfed quite a bit myself for five years. Surfing is an amazing fitness tool - you've got the resistance training aspect of swimming, plus co-ordination, plus HIIT. If you're getting two good sessions in the waves a day (and because you used to compete, I'm presuming that you really go for it) then you are definitely living an active lifestyle.
First question everyone's going to ask is: how many cals are you consuming a day?
Also how much fat are you eating? The whole primal paradigm is based on eating fat in favour of carbs, but if you hang around the forum for a while you'll hear people's personal experiences, and many of us (younger women particularly) do not do well on high fat low carb.
For someone as active as you, I'd recommend shifting your diet in favour of carbs. You'll get more out of your sessions, and as long as you keep your total calories in check you'll lose fat.
Unfortunately the belly is the last place to go, and sometimes it can take years of honing the diet to get there.
One more thing: you said you were on GAPS. Do you have gut issues? If so, part of your belly may be bloat. Not necessarily good news, as this can be just as hard to shift as fat...
Welcome to the forum
Ps. Where do you surf?
"I think the basic anti-aging diet is also the best diet for prevention and treatment of diabetes, scleroderma, and the various "connective tissue diseases." This would emphasize high protein, low unsaturated fats, low iron, and high antioxidant consumption, with a moderate or low starch consumption.
In practice, this means that a major part of the diet should be milk, cheese, eggs, shellfish, fruits and coconut oil, with vitamin E and salt as the safest supplements."
- Ray Peat