My guess is you are using a low stretch string like poly. Start with you weight down and left it slowly in small increments and let it down slowly.
But then how do you clamp a single string with flying clamps. if you had a starting clamp you could clamp the right main outside the frame with the SC and tension the left main then you have two strings to clamp.
I would like to apologize to anyone I have not offended. Please be patient I will get to you shortly.