You are at the toughest mode click/second game. Because you have to continuously click for 100 seconds here. If it sounds funnier to you then try it first and then see how difficult it is. You can not even maintain 6 CPS above here. If you want to make a decent score here then follow the given guidelines.
Guide for 100 Seconds Click Speed Test
Start with a relaxed mind and slow clicking. Maintain 4 CPS for the first 50 seconds. After then for the next 35 seconds, you should accelerate your speed and make an average of around 5 CPS. For the last 15 seconds, you should click as fast as possible. This is how you get the best out of this marathon test.
If you have a laptop or touchpad with your mouse then you can click on both. So you can get around 10 CPS in 100 secounds.