I dont use long strings for that very reason. Get it bending as even as possible at floor tiller then i go to a very low brace, maybe like 1 inch and begin testing the bend.
Also i agree with the above. Start taking wood away from the handle. Leave the handle alone until you get the limbs bending then get the handle bending in the last couple of inches of draw.
I like to see my handles bending not just feel them. Seems you are the same way. Looking forward to seeing this one finished. Don't rush. Take breaks