Hyde here from Shopify.
Congratulations on all the work you've done so far. I understand your concern but don't worry there are a few things to know to keep your work secure:
1) The trial itself is not intended for anyone to complete their store. The free 14-day trial is for new store owners to familiarise themselves with the platform and how it works. Building a successful store will almost always take more than a mere two weeks.
2) That said if you feel like you need more time on your store you're welcome to reach out to our support so that they can have a look at whether they can help you in that respect.
3) You could pick a plan before that trial of yours runs out! Take a look at the available plans here. If you're on a plan when your trial ends then you won't experience any downtime on your store and can continue building it!
4) Of course, if you haven't picked a plan then we can only guarantee that we can retain your content for up to 30-days after the store has closed.
I hope this all helps, let me know if you have any more questions.
All the best, Hyde.