Sentence: "We
should/must remeber 9/11 not because of large number of people were killed in it but because the way they were killed."
My question/doubt: I used the verb "should" in the above sentence
inflowof writing, you know, but later I realized verb "must" would be much better in place of should. So my question is (A) Does my usage of should make the sentence wrong ? (B) Has the meaning of sentence changed because of the usage of should ? (C) Give any input you have regarding this

Thanks