ついうっかりしてバスを乗り間違えた。

just (now); quite (near); unintentionally; unconsciously; by mistake; against one's better judgement (judgment)

carelessly; thoughtlessly; inadvertently

bus; bath; bass

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to get on (train, plane, bus, ship, etc.); to get in; to board; to take; to embark; to get on (e.g. a footstool); to step on; to jump on; to sit on; to mount; to reach; to go over; to pass; to follow; to stay (on track); to go with (the times, etc.); to take part; to participate; to join; to get into the swing (and sing, dance, etc.); to be deceived; to be taken in; to be carried; to be spread; to be scattered; to stick; to attach; to take; to go on

to make a mistake (in); to commit an error (e.g. in calculation); to confuse; to mistake something for something else