There are many ways of writing this. "Wednesday, March 28th, 2018" is probably the most common and is universally (I think) acceptable. "Wednesday 28 March 2018" is more formal and is usually only seen in legal documents. "Wednesday the 28th" is common in spoken English when the month and year are obvious (often when making plans with friends). Sometimes in written communication you'll see "Wednesday" abbreviated to "Wed." or "Wed"; this is perfectly acceptable in writing, but sounds strange in spoken English. "Wednesday, March 28, 2018" is OK, but "28th" is preferred over "28".
Don't forget the comma after "Wednesday."
Note: I'm from the U.S., this may not be the case in the U.K. or other European countries.