Disappointment in my Khan Academy SAT practice scores vs College board SAT score

To whomever this may concern, 

I am extremely frustrated with my experience of Khan Academy's SAT practice preparation. For the past 8 months I have been studying for 20 minutes a day as well as taking a full practice test every month provided from your websites exam option. I was very happy with my scores being all over 1150 most consistently 1200's. I went into my official October SAT feeling very confident just to get my score back as a 1050. I am extremely disappointed, and unsure of how my score could have dropped by that much. I was taking all my practices honestly, under correct timing, and in a good environment. Is there something wrong with the Khan method that has lead to this misinterpretation of my score. Please write back to me as soon as possible with any suggestions to my problem. Perhaps I should consider taking another SAT prep course.

Thank you.