You have: 30 days right of return, if unopened.

LEGO Giant Mystery Box - Surprise package full of building fun contains a customised selection of original LEGO® bricks and elements. The exact composition varies and may include pieces from different themes such as Classic, City, Friends, Technic, Minecraft or DUPLO. These are not complete, sealed LEGO sets with instructions, but a mixture of bricks that allow for creative building fun.

The LEGO Giant Mystery Box - surprise package full of building fun for the whole family usually contains complete LEGO sets, not individual loose bricks. These sets are usually in their original packaging and can come from different themes, such as LEGO City, Friends, Ninjago or Creator. The exact content varies and is not predetermined/known. Hence the name Mystery Box. Unfortunately, returns are not possible. See here: 30 days right of return, if unopened.