Too expensive. And the magnetic containment system would be prohibitively complex. Besides, where would I find dilithium crystals? The Chinese have that market cornered.
First of all the dilithium mines on Rura Penthe will supply all you need and the miners are all slaves so they can pass the savings on to you...the consumer. (There....I used ST and Firefly references )
Secondly ...You don’t STORE antimatter. You manufacture it by taking matter particles and teleporting it via Quantum Entanglement and reversing the electrons to positrons during the process directly into a rocket nozzle where a gaseous matter is being pumped.