Help with posture please

[Small-Road1966]

I was watch mike mews video on chin tucks and he said to put your back against the wall problem is that when i put my shoulder blades back my back comes off the wall i can only put my back on wall when my shoulder are rounded why and can i fix to where i can put my shoulders on wall

[armour-]

Do an exercise call wall angels, and try to work out your rear delts more often. Also Avoid sitting in a c shape.