In the second photo, your "top stretching arms" are not in proper position. The lower part should be slid to the awning roller tube and extended to stretch the awning so it is tight. There is a "locking knob" on those "top stretching arms" that will maintain tension on the awning fabric.
When you do set it up properly, be sure that if there is any chance of rain, to lower one of the "diagonal side arms" so your awning "dips on one end" so the rain water can drain off the fabric. One of the fastest ways to destroy and awning, pull the awning rail away from the trailer sidewall, causing it to leak and cause trailer rot is to allow rainwater in any large quantity to remain on the awning fabric. Each gallon weighs about 8 pounds, so 50 gallons of rainwater would place a "400 pound pull" on the trailer awning rail. If it doesn't pull the rail away from the trailer sidewall, it will likely bend/break one of the awning sidebars.
Anyway, all that said, those two "sliding bars" will lock in the top of the large side arms (at the roller tube) and can be adjusted to stretch the awning fabric so it's tight and doesn't sag.
Here are a couple of pictures of what I'm talking about and here is a "generic how to" describing what you "should be doing".
https://www.wikihow.com/Open-an-RV-Awning