In reference to these results for this survey
This poem is a mnemonic. The mnemonic is used to answer the question "how many days are in this month?"
If it's February, you're never going to be asking that question, because you already know how many days are in February. (Or if you don't, you need to look up whether the current year is a leap year, or find a different mnemonic; the poem won't help you.)
So for example, it's June. I might not remember how many days are in June. So I'll quickly recite in my head (or aloud, if I want to help my cat remember too:) "Thirty days has September, April, June, and November." Aha! I said "June", so the month I'm in only has thirty days. If I ever don't say the name of the current month, I know it has 31.
As everyone commenting on the survey is quick to point out, there is no elegant way to incorporate February into the meter or rhyme scheme. So don't! You don't need a mnemonic to remember February, because you already do!