There are loads to of threads about the Libre falling off.
Many people find it useful to wear something like Tegadrem or Vetrap to hold their sensor in place whereas other find they are more adhesive.
If you have problems such as the sensor falling off before it reaches the end of life, call Abbott. They often replace the sensors. Do not throw your sensor away until you have spoken to them as they may request you return your sensor.
If you are new to Libre, I strongly recommend reading through the threads to understand what others have found works with regard to stickiness, allergic reactions and accuracy.
There is too much to rewrite here. Just use the Search field in the top right of this page to find the threads.