How much poetic license can one use in an autobiography?

When people read an autobiography (or biography) they expect the work to reflect the facts accurately. How closely and so on will depend on the kind of autobiography, but the scope for 'poetic license' is very limited. Otherwise, the autobiography will become a - potentially confusing - work of fiction. In English literature (unlike French literature, for example) there is no tradition of writing 'embellished' biography, and it is usually not popular. The same hold for autobiography. In fact, if you write about your own life, authenticity is something that readers usually value in particular. One of the few exceptions is T. E. Lawrence's 'Seven Pillars of Wisdom'. However, the element of fantasy in the book is almost universally criticized as a fault, and it's even been said that the author had some psychological problem that prevented him distinguishing fantasy from reality. So, I'd urge caution.