I really like it! I would suggest you to optimize your pictures. It took me a LONG time to load your main page. You should check your page score at Google PageSpeed Insights.
Congrats on launching your site. You've got some great designs and it looks like you're on the right path to success.
Couple things I noticed shown in this screenshot of your mobile version and applies to the desktop version as well:
1. There is a lot of text in the header. Most people will probably not take the time to read it and will simply look like clutter distracting them and taking away focus from the product. I would limit yourself to one line of text in the header.
2. Having the title of the product is good, but there isn't anything compelling me to want to click 'View Product'. This is a great blog post about copywriting that you might find useful.
3. I find this image doesn't showcase the t-shirt in the best way. You might try an image that features the design in a slightly better light and at a better angle to so visitors can see the shirt better.
Hopefully, you find this feedback helpful!
I'm curious to know: What is your plan for bringing traffic to your store?
Add some space between cart and currency switcher.
Too much vertical space, do you really need it ?
Tab title annoying animation, imho it is really annoying... )))
Product option names are not highlighted properly, so the customer can see it and chose color or style, make different color or different font or make them bigger...
Too heavy footer on mobile, it takes almost 40% of vertical space, I will suggest remove "someone has just bought" app at all, at least for mobile.