Sorry for the delayed response.....
Here is the recordings of expected and actual behaviour.
I had made the selection mode as single and also had used merge cells, in that case selectionmode single is not working, I can able to select the as many cells I can. But If I remove the merge cells then it's working as expected.
Here I had removed the merge cell and now it's not allowing to select more than one cell.
My expectation is, I need to use merge cells and the selection mode should not select more than one cell.