Excel - how to fill blank cells with value from above

Hello

I have a spreadsheet with approximately 300 rows of data and I need to fill in the values in the blank cells based on the rows above. Online it says to do this by selecting the blanks, which I've done, then I enter =A2 in cell A3 and press control and enter at the same time. However, I've done this and what happens is that the values aren't copied but instead it enters =A2 into each blank cell. I'm sure I must be making a stupid error / mistake but i can't seem to figure it out. Please can you help?