The poem is called "Weep Not For Me." It is in ballad metre which comprises couplets of tetrameter (four feet) and trimeter (three feet).
The trouble is that the sixth couplet seems to consist of two tetrameters, which throws the rhythm off as there are two extra syllables in its second line.
Line twelve as written is
In your memory I live onbut I will deliver
In mem'ry I live onto preserve the shape.
At least no one can accuse me of failing to prepare.