I accidentally dropped the wrong player (starting ss vs bench pitcher). Is there any way to cancel transaction and if not, my ss isn't showing up on the list of available players. Are we able to reclaim our own players we dropped or is there a waiting period?

in a theme league, if you got the league's approval you could probably get the commissioner to submit a ticket to undo the transaction. for an open league, you could try submitting a ticket, but I'm not sure they'll let you undo it.

also unless you have cap space you won't be able to reclaim him without paying the 10% transaction fee, which is assuming you can reclaim your own players, which I'm guessing you can't.