Go ahead and accept the AROTC Scholarship. In the event you win the MO Scholarship, you simply decline the AROTC via the portal if you choose the MO. A word of advice, don't decline a scholarship until you have all of the boxes checked (DoDMERB...). You won the scholarship, decline it on your own terms if you have options. Some people here will say - decline your scholarship so it will open up to another candidate. That is not how it works. A declined scholarship does not open up a slot for someone else. The un-used funds are re-distributed for campus based allocations.
MO could be late March/April before final notice. Last year my DS was notified of the MO Scholarship on 5 March. My DS waited until the week before school started to decline his AROTC.
Congrats on your scholarship. Well done!