Excited having placed bet on ace (8)
I believe the answer is:
aflutter
'excited' is the definition.
(similar in meaning)
'bet on ace' is the wordplay.
'bet' becomes 'flutter' (to have a flutter is to put a bet on).
'on' means one lot of letters go next to another.
'ace' becomes 'a' (abbreviation).
'flutter' put after 'a' is 'AFLUTTER'.
'having placed' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for aflutter that I've seen before include "Nervous, twitchy" , "is rather nervous" , "Agitated - excited (eg in anticipation)" , "trembling" , "in excited state" .)