4 week moving average

Hello,

I am new to Power BI. And I am trying to create a column with a 4 week moving average. I have been reading other posts about the topic, which hasnt been perfectly helpful, but I tried putting it all together. However, I will either get an error in my new column, or like in the picture, I just end up replicating the orginal values from the Weekly Data column. My ReCreate column is trying to reproduce the same values that are in the 4weekMA column, which is caluculations I did from my excel of the Weekly Data and is correct. In the screenshot, the for 4 rows don't need to have a 4 week moving average, because it wont, so I crossed them out. The data after that in the ReCreate column should match the same numbers in 4weekMA column, and those numbers are just the 4 week moving average of the Weekly Data. This was meant to be a simple exercise for me, but it's proven to be difficult. 

I will appreciate any help on the matter. I must be overlooking something simple or leaving out some more code. I feel like I am close to my goal. Also, I have been having trouble doing a year-over-year column as well.