Fully fit? I agree (4,4)

I believe the answer is:

very well

I'm a little stuck... Click here to teach me more about this clue!

'i agree' is the definition.
(I've seen this before)

'fully fit?' is the wordplay.
'fully' becomes 'very' (I can't explain this - if you can you should believe this answer much more).
'fit?' becomes 'well' (associated in meaning).
'very'+'well'='VERY WELL'

Can you help me to learn more?

(Other definitions for very well that I've seen before include "said by some to be obliging" , "Blooming" , "Agreed" , "if you want" , "okay" .)

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.