Well believe me when I say I tried EVERYTHING before I got to the right thing. I looked at:
Final E in grid in clues, Final Y in grid and clues, Final ly in clues, Things that went on or lasted forever (like Pi, the Messiah, Dvorak symphonies, characters voiced by Mel Blanc), PI
Circumference / diameter[--]
Closed-topped fruit pastry[---]
(since you seldom do two letter answers I was suspect), Words with "ON" in them to see if there was ON and ON.
FINALLY (yes, reference intended) I went back to my forever idea and while looking up the half life for scandium (and finding it to be hours instead of eons...stupid non-radioactive isotopes) I went back to SCANDIUM
Element with atomic number 21[--------]
again and instead landed at SANDPIT
Playground feature involving buckets and spades[-------]
. "Idiot" I proclaimed, but I saw how I could do that since it had an AND in it....WAIT A MINUTE NOW! So there were a preponderance of ANDS, plus they were symmetrical; clever boy Ben. Of course my first answer AEPOIMIL (which Webster's defines as "Inability to solve a meta crossword despite having the right idea") was wrong but "ultimately" I saw my way home. Now here I was going to say, and finally - and then go on for another paragraph or two, but instead I'll just say "Thanks for a puzzle with long lasting enjoyment"