I wrote a little haiku...

No, it doesn't follow the traditional structure of a haiku. A haiku is typically a three-line poem with a syllable pattern of 5-7-5. Let's check the syllable count in your poem:

Line 1: I've got lot's to say (5 syllables)
Line 2: But my brain is a funnel (7 syllables)
Line 3: Ne'er thought it that way (5 syllables)
Line 4: Til it came through the tunnel (7 syllables)

It has an additional fourth line, and haikus traditionally consist of just three lines.

This is a haiku:

So much left to say,
My thoughts funnel through a void,
Emerging anew.

Pretty good!