You stop the sanctions by meeting the new demands. The US decided the original deal did not offer inspectors enough leeway to ensure Iran was actually halting nuclear weapons development, and so it added more stringent inspection requirements. Adopting or walking away from a deal is a mutual decision. Yes, the US decided to put new terms on the deal. Iran could have accepted adding real enforcement mechanisms to the deal and ended the sanctions, but decided otherwise.

This thread is being rate limited. The commenter below is incorrect. The post deal demands included restrictions on nuclear-capable ballistic missiles, too, but they also included changes to increase the access of inspectors. This was a substantial part of why the original deal was rejected, the new administration believed the original restricted inspectors to the extent that Iran could still develop nuclear weapons in secrecy.