Few of us really believe we are ready for solo, although some do, when they are not.
It is a psychological barrier that we all go through to the next level of learning.
Looking back on it we all wonder what we were so worried about.
Your instructor would have a very good view of your ability and would never send you unless you were ready - and then some. But, if you truly believe you are not ready, then don't go.
I'll never forget my first solo, when the instructor climbed out, secured his straps and said "she climbs a lot better without me in it".
I had little time to worry and the feelings -exhilaration, terror, joy, panic -still live with me 42 years later.