I think that I'm afraid to quit my job
That's a normal feeling. What scares you about quitting?
I'm afraid I won't be able to cope with the new job if I quit now. It would be an awful experience
If you found a better job, good for you. It does seem scary since you're used to your old job, but if you have better opportunities you need to take it head on. You don't want to be plagued with "what-ifs" all the time.
I will look for a new job, thanks.
No problem, you are just worried about the unknown which is perfectly okay. You will never know what is better for you if you don't get out of your comfort zone! I wish you the best in finding a job more suitable for you.