Acetaldehyde with few drops of concentrated sulphuric acid Acetaldehyde on treatment with a few drops of concentrated $\ce{H2SO4}$ gives?

Attempt:
First, I formed an enol intermediate in acidic medium $\ce{CH2=CHOH}$. Then, I performed electrophilic addition of another acetaldehyde molecule on this enol intermediate to get $\ce{CH3CH(OH)CH2CHO}$.
But answer given in my book is:



Please let me know the error in my attempt.
You're not wrong.

Your mechanism describes the classic acid catalyzed synthesis of 3-hydroxybutanal by dimerisation of acetaldehyde (Borodin 1869, Wurtz 1872).


Image: Whoopie23, Wikipedia

However, under different conditions acetaldehyde forms different addion and condensation products. E.g. with concentrated sulphuric acid at low temperatures metaldehyde is formed whereas at room temperature paraldehyde (the answer given in your book) is formed.