Rear disc brakes on Laguna 3
RENAULT

Describe your problem more precisely, it’s not entirely clear what the problem is.

yeah, It can be frustrating when things don’t go as smoothly as expected, even with the help of YouTube videos. It’s good that you checked the hand brake, but there are a few other things to consider. Are you sure that the caliper is the correct one for your vehicle and that you have the right tools for the job? Is the brake fluid level in the master cylinder reservoir low or high? It’s important to read some info here and  check these things as they can affect the brake caliper’s performance  https://www.bikethesites.com/hydraulic-vs-mechanical-disc-brakes/ If you’re still having trouble, don’t hesitate to ask for help from a professional mechanic or a more experienced friend.