唔該幫我轉英文呀

This is how I would say:

我想訂張檯6/7 6 位
I want to book a table for 6 for July 6.

可唔可以到時拎個蛋糕放到你們處, 要否收切餅費?
Can I bring a cake and keep it at your place (fridge), any extra charge for it?

到左 6/7, 去到門口, 想講話訂左張檯6 位及(到時會) 比個蛋糕佢幫我Keep
I have booked a table for 6 for 7pm. Please keep my cake at your fridge.

想叫佢拎個蛋糕出黎
Please bring out the cake which I kept at your fridge 跟住點講

可否幫我切開 6 份
Would you cut the cake into six pieces for me? Thank you

埋單
Can I have the check (the bill) please?


PS. Normally it's 'on' the date 'at' the time. But it is easily be mistaken as the date/time to make the request rather than the date/time when the request is for. And honesty this is not an English exam, as along as the waiter understand then it would be good enough. And I think your own translation is fine.