Four points.

(1) Unless you want to just flash by Alpha Centuari, you are giong to need and an equal batch of fuel to decelerate once you're halfway there.

(2) Calling it "antimatter" is understandable if one sees the mass disappear and one doesn't understand energy-mass conversion. "Anticharge" would have been more accurate. But this raises the fascinating question: why is charge the key to converting mass into energy??

(3) What form does the 98% of matched anticharges take. Seems like a good "dark" candidate. And was the slight imbalance the same for all anit-pairs?

(4) You assume Semites will exist in an anti-matter-verse. Seems as unlikely as any other earthly thing so existing, no?