Hey there! I don't know about this scan to be honest
- it's pretty flat BUT it's not completely horizontal - leaning more towards that 30 degree angle upward indicating boy but I'm new at this and I've been learning little by little so don't hold me to that. 
I'm on the fence. I think maybe girl but the angle of that nub is making me think maybe boy too - I'm sorry I"m not that helpful. The one thing I do know is that my u/s tech told me that even at my 13 week 2 day scan, ( I thought I saw 3 lines too) - she told me that it's way too early to see the 3 lines and that at an 11-13 wk scan - they only go by the angle of the nub (vertical more than 30 degrees is boy and less than that would be indicating girl) and if it looks like a turtle (boy) or is completely flat (girl)
Good Luck and keep us posted!
Monica