On the whole, critical illness insurance is worth buying. There are usually dozens of major diseases. I don't know if yours is true. If you really want to surrender, you should provide a cash value table when you buy insurance, which is the surrender amount. Just do a simple calculation. Generally, it will be less than the principal, and the sooner you leave, the less.
Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.