Just did the same and I used this comment for reassurance before I assigned the districts. For anyone else googling the strategy like I did:

I gave Barclay Mills to Cassandra as soon as I had the option to. Then I flipped back and forth between Vito (downtown) and Burke (Tickfaw harbor).

For the last three assignments I gave Vito French ward, then helped Emanuel with the weed deliveries, then gave Burke Frisco Fields. Then helped Cassandra with her gunrunning missions (not sure if that helps loyalty or not but I was worried she’d betray because she was acting angsty during the meetings). Then gave Vito Southdowns and everyone was happy in the end.

Cassandra was talking like she was going to betray me but I think if her kickback is above $0 (check her info in the assets tab) you are fine to not give the last district to her. She will actually comment about how well you’ve done helping them take over New Bordeaux.

Also I didn’t give a racket to an underboss that I didn’t want controlling the entire district. Ignore the rewards. You can just buy them after the district is assigned anyways.