Just a sticky mess, but it won't come to nothing! (3)
I believe the answer is:
goo
'just a sticky mess but it won't' is the definition.
I know that 'sticky' relates to this answer.
'come to nothing' is the wordplay.
'come' becomes 'go' (synonyms).
'to nothing' becomes 'O' (O resembles 0).
'go'+'o'='GOO'
Can you help me to learn more?
(Other definitions for goo that I've seen before include "Substance that's viscous" , "Sticky substance (sl.)" , "Sticky matter" , "Sticky gunge" , "mud, for example" .)