Do we even have a contract if I signed an roofing contract, cancellation paper and the addendums on the same day?

Without reviewing the actual documents, it is not possible to make a determination.

A promise is sufficient to create a binding contract. Without reading the contract and cancellation, it appears that the contractor did not have sufficient time to purchase shingles or make arrangements to begin work. A $100 dollar cancellation may be reasonable and not worth arguing about, and it appears that this contractor is attempting to strong arm you. I suggest that you explain to the roofer that you will not be paying any 35% cancellation charge but will instead refer the matter to your attorney if necessary.

I have represented a lot of home owners and contractors, and this is not a provision that I believe would be found enforceable.

I would have to review the contracts and the factual situation. Generally a contractor will have a lien on your house and is required to give you three days to rescind a contract which would cause that to happen. If you complied properly there should be no contract. If you did not it is quite possible that the contract does have a penalty clause for cancellation. See an attorney.

Contact an attorney.. that sounds like a scam.