I'm going to cancel my plans with friends this weekend
Is there a reason why you plan to cancel the plans you made promises on?
Not really, I just don't want to go.
You can't just change your mind because you feel like it. It's rude and disrespectful to those you make the plans with and it makes you look unreliable. People don't like friends that don't keep their promises.
Sorry, I don't think I should be trapped doing something I don't want to do.
I can understand that, but that's something you should have considered prior to making the plans with your friends. If you cancel like this, your friends might never invite you to do fun things with them in the future. Maybe just go and try to have as much fun as you can.