Cal here from Shopify, thanks for reaching out to us. You've made a great start on your store! I've taken a quick look and have some points for you to consider:
1) Domestic Shipping: specify what this means, as you may have customers from anywhere in the world. Is it free UK domestic shipping? Or free US domestic shipping?
2) Product photography: it would be great to see some modeled photography showcasing the products on the landing page, rather than all stock photos.
3) Blog: creating a blog centered around martial arts and taekwondo would be great for your SEO. You should consider adding a blog to the site, which would also give visitors extra content to return for. You can read more about blogs here.
4) Market test your site with your target demographics: the best feedback usually comes from those who you would expect to buy on the site. I would group test both men and women, and get their individual perspectives.
5) The 10% off promotion is great, but have you considered using it to encourage signups to your newsletter? An app like Privy can help you create a delayed pop-up encouraging visitors to sign up to marketing communications in return for the 10% off.
You've made a really great start to the site! How are you planning to market it to your target demographic?