The next election isn't due until 2022 (not 2021), but we've already had one early election, and a minority government tasked with the enormous and divisive role of delivering Brexit is presumably quite vulnerable to yet another early election. I certainly wouldn't be surprised if there were one next year, for example; although more likely it would be something like a few months after "Brexit Day" in March 2019, after which point there's no longer any reason for the Tories to pretend to be united.