That’s how consulting usually works. You scope out stories and commit to the number of stories in a sprint. Even if you wanted to add more to the sprint you’d just mess up the allocated time of QA and add more stuff for the dev ops team. That’s why more than one person (and people who know the system) should be giving estimates.

Otherwise, if it takes half the time use the other half to test, or train yourself to be better at your job. IMO