The verb "to close" indicates that something is changing state from being open to being closed. This is usually something that happens fairly quickly, and after that the thing is just "closed". Using the present continuous form would mean one of two things:
- The process or activity of closing has been going on for a while up to now, and it still isn't actually finished yet (it never did become fully closed).
- The shop has been repeatedly closing over and over again over a period of time.
So, for example:
That store says it's going out of business. It's been closing for two weeks now but it still seems to be as busy as ever. (sense 1)
The store usually closes at 9pm, but they don't have enough staff, so it's been closing early for the past few days. (sense 2)
However, in the case of your example, you probably didn't intend that your shop is still in the process of closing (it presumably closed two days ago and has stayed closed ever since), and you probably also didn't mean that it's been opening and closing repeatedly over those two days, so in this case what you want to use is the present continuous tense of "to be" (expressing a state, not an action) with the adjective "closed" (or "closed down"), instead:
Because of the COVID-19, my shop has been closed down for two days.