Sometimes there could be injury
to the salivary duct opening leading to this mucus cyst
the Dr has told you about. You need not worry as long as there isnt any pain or increase in the size of the swelling. Take plenty of water, sour foods and do some hot fomentation to the area this will make it heal faster. If the swelling persist and troubles you then better to visit back the same Dr who operated you.
I hope you found my response to be helpful and informative. If you have any additional concerns I would be happy to address them.