Hello,
Thank you for asking your query at DoctorgSpring.

I understand that your bag filled up as you forgot to empty the bag. Usually this won’t cause any problem, provided you bag is rather clean and its happened only once or twice.
The main risk here is the possibility of a retrograde infection. In case your bag has some bad bacteria it can travel back into your urinary tract or bladder and cause infection there. But if you maintain proper hygene the chances are pretty less. Contact your GP in case you experience any fever, rigor, chills or pain.

Please do follow the following precautions regarding emptying your bag.
Emptying your leg bag
• Do not let your leg bag get too full and heavy as it will pull
and damage your body.
• Empty your bag when it is two thirds full.
• Empty your bag into a clean toilet, jug or urinal.

Thank you
Hope this helps