stuck in lvl15 Map bug report number 2350210501 user Robbbo1#6769

Hi I entered the boss arena on lvl 15 Rugosa Map and the boss spawned then dove back into the pool never to re-appear now i am stuck because i cannot create a new instance as its not an option.
I have logged back to character selection and also all the way out of game and exited Steam only to find when logging back in i am still in the map bosses arena. please help me continue many thanks Phill