Your example sentence
Beware—you do not intend offense.
does not have any obvious problems with English Grammar. It also doesn't feel like it is an awkward sentence.
Another thing you should also keep in mind when writing poetry (or prose) is that when writing them they are allowed leeway in breaking grammatical and sometime spelling rules in the name of art, especially if breaking those rules helps the poetry to convey meaning beyond what a correctly written English sentence would. As an example, I quote from Lewis Carroll's 'Jabberwocky':
'Twas brillig, and the slithy toves.
Did gyre and gimble in the wabe:
All mimsy were the borogoves,
And the mome raths outgrabe.
In this example, although he used English sentence structure, most of the words are made up (i.e. not real English words). Art is about experimenting with the medium, (in the case of poetry the medium is language) even if it offends or annoys possible critics. Knowing how and when to break established rules is a good thing though; a rule broken unknowingly will often result in something that rather than being artistically experimental, shows instead that the writer was unaware of the rule(s) they were breaking.