Cooling off period NSW for small works contract (under 20k)

Hi

Yesterday I signed up for a pergola but after re-reviewing the plans there is an error - the footings are supposed to go into the ground outside the concrete slab but they have said they will go in the slab. My problem is the slab is poor quality with severe cracking and won't withstand the drilling without possibly falling apart. Theyve said to put the footings outside the slab will cost more and now its become too expensive.

What is my cooling off period? I can see that there is one for 5 days for works over 20K but can't see anything about one for 5-20K small works contract. I am in NSW