Blanket Calculations

I am on my fifth and final skein of yarn for Jack's Blanket and now the anxiety comes . . .

I need to end on row 12 or row 24 AND have plenty of yarn left over for 10 border rows. I have never been good at estimating yarn. I tend to run out right in the middle of the row. I'm taking the risk to go to row 24 then work the border. My measurements estimate about 8 pattern repeats plus both borders to be 90 cm. I may have more yarn left over than desired but it's better than not having enough!