Power BI is Not summing up correctly

Most likely, Power BI is doing exactly what you are telling it to do. Remember that measures are evaluated within their current context. So, a measure in a table will not simply provide a sum of the rows displayed in the table, it will evaluate in the context of essentially ALL of the data in the dataset. So, you need to design your measure a little differently if you want to use it in this way. I believe I have a post on this in DAX Commands & Tips forum. Yep, here it is:

http://community.powerbi.com/t5/DAX-Commands-and-Tips/Dealing-with-Measure-Totals/m-p/63376#U63376