The effectiveness of the patch is the same as the pill with perfect use. So if you use it exactly right, without making any mistakes, it’s very unlikely (less than 1% chance) that you’ll get pregnant.
If you make an occasional mistake when using the patch, it’s slightly less effective. So it is possible to get pregnant if you forget to change it and don’t remember for several days, or if the patch comes off and you don’t notice.
The best way to make sure it is effective is to follow the instructions.