You, my geological friend, do a fine job of keeping your low back in extension. You have a pronounced kyphosis, however. I have two pieces of good news for you. 1 – you are not going to really be able to change that. 2 – it is an advantage on the deadlift. Your bigger problem is that you are not following the steps for the deadlift. Stop banging your shins into the bar immediately before you pull. Shins touch the bar. Knees go out. Arch the low back. Big breath. Drag the bar up the legs. You are doing the following: bring the shins to the bar, pray for a miracle, stand up. Also, you didn't really fail that lift. You just didn't really go after it. Do the steps. One at a time. Stop rushing. Embrace your kyphosis. Anticlines for the win.