CEO & CTOSince we've had a couple of reports about this, I'm now writing this thread to clarify.
It is now possible to race in sprint races with two cars. Simply check the two cars option at the top. This is probably on by default for most of you unless you are in a one-car league.
The simulator had to be prepped for this update. It was technically quite challenging to allow some teams to run two cars and some teams to run one car. I've now worked around that and it's possible so it's live!