The unusually frequent use of slant rhyme (4 in total) in a relatively short poem might be a sign of purposeful errors that John Donne makes to implicitly express the excitement and satisfaction that the speaker is experiencing that he doesn't bother about strictly keeping the formality.

The poem contains four slant rhymes, which is an imperfect rhyme with similar, but not identical sounds. Most slant rhymes are formed by words with identical consonants and different vowels, or vice versa.

lines 1 and 3 - "I" and "childishly"

lines 9 and 11 - “fear” and “everywhere”

lines 12 to14 - “gone,” “shown” and “one”

lines 19 to 21 - “equally,” “I,” and “die”