Tesla’s first-quarter production figures underscored two things about the maker of electric cars: The company seems to pack lots of activity into the final days of its quarters, and it keeps having trouble meeting its hugely optimistic targets.

Tesla said Tuesday it had produced 2,020 of its Model 3 sedans in the previous seven days. What few noticed is that production for those seven days (which actually extended a bit into the second quarter) amounted to 21% of all the Model 3s Tesla built during the first quarter. That’s...