Obviously a 600 column table is inappropriate, because tomorrow it will be 601.
Sounds like about three tables with just a few columns each.

user table
    user_id
    user_name, other login details
    (index user_id)

question table
    question_id
    question
    answer
    (index question_id)

answer table
    user_id
    question_id
    answer
    (index user_id+question_id)
[download]