Check the size of your mattress. Unlike the top sheet or your duvet cover, fitted sheets should fit your mattress very, very snugly. Linen tends to sag and you need a very tight fit. Check that your mattress is 200cm long because there are also 190cm long mattresses and it is very common that we have never noticed.
![Linen top sheets](http://delenzo.es/cdn/shop/collections/05620.jpg?v=1674671450&width=1700)