There's not a lot to do for the 4th week in the event. I finished without any trouble. There was a space of time where I had to wait for the last task to pop up though. To find event items, filter Show All by Special--Event Rewards in Buy Mode.
The cake is a Birthday Cake. Most options are for sims to age up, so be aware of that! You can choose to light candles for a birthday and to celebrate. You can eat the cake, but I don't think you can after the cake is used to hide in. (?)
Your sims has an option to hide in the cake and jump out in whatever outfit you choose for them.
Then they dance while others celebrate.
The dance is the old Smustle.
Once the cake was used, I only saw options to celebrate or clean up.
As nice as it is to have an option to have our Sims be able to do the surprise now, I still think there should be an option to hire an entertainer to pop out of the cake like in the original. The entertainer doesn't have to wear a flirty outfit while doing a flirty dance. They just need to pop out, wear appropriate party clothes and dance. (That and the chance of a more ridiculous surprise depending on how the party is going.)
