Correct spelling, explanation: ignore is borrowed from the Latin ignorare. As you can see, the word did not change much, it only lost the typical Latin ending -rare, which is typical for verbs of Latin origin. As to why there is still e at the end – it’s most likely due to the fact that ignore was introduced to English not straight from Latin but from the French form ignorer. In this form, the last r was not pronounced, but e was still important, and because of that it has stayed in the modern English form of the word.

Definition of ignore:
verb
1. to act unaware of something or someone
I tend to ignore the signs of the flu until I’m too sick to work.
The government seems to ignore the needs of the homeless and needy.

Incorrect spelling, explanation: ignor kind of fits the pronunciation, but remember that it is not a correct spelling of the word ignore. Sure, the e at the end of the word is silent anyway, but because the word had been introduced to English from French, the e is the remainder of this past, and a generally recognizable pattern in many English verbs. And, even if you just look at it, you can see that intuitively ignore simply looks much more proper.

Incorrect spelling