Great Weapon Master Can Give Me 120 Bonus Damage

We rolled for stats in the campaign I'm in and I rolled 18 Str 17 Con and 15 for all other stats so I went half orc to bump my Str and Con to 20 and 18 for my fighter back up which started at lvl 5 (Party lvl). so I chose the Feat great weapon master to allow for more great sword damage and realized that if at lvl 20 I action surge with the four extra fighter attacks and so did my echoes that we would all attack 8 times and because of great weapon master you add proficiency bonus to heavy weapon attack damage. Ao I would get 40 extra damage and so would my echoes so 120 in total.

I think you have misread that class.  20th Echo Knight gets 2 Echoes, you get 4 attacks, plus 1 for Unleash Incarnation which can come from either echo.  With Action Surge you will gain another 4 attacks and 1 more attack from one of the Echoes.  So 10 attacks, assuming all hits gives 60 additional damage.  (PB is +6 at 20th level.) 

Echoes are not Simulacrums that act as a player character, they are much more restricted.

Still pretty good though!

Quote from DarkBoiDruid >>

We rolled for stats in the campaign I'm in and I rolled 18 Str 17 Con and 15 for all other stats so I went half orc to bump my Str and Con to 20 and 18 for my fighter back up which started at lvl 5 (Party lvl). so I chose the Feat great weapon master to allow for more great sword damage and realized that if at lvl 20 I action surge with the four extra fighter attacks and so did my echoes that we would all attack 8 times and because of great weapon master you add proficiency bonus to heavy weapon attack damage. Ao I would get 40 extra damage and so would my echoes so 120 in total.

As has been pointed out in the other thread you posted about this, the Echoes are not creatures that get their own entire turn with all of your abilities. They don't have the ability to take actions, use Action Surge, or anything else. You can make one extra melee attack from an Echo's position.

Quote from DarkBoiDruid >>

We rolled for stats in the campaign I'm in and I rolled 18 Str 17 Con and 15 for all other stats so I went half orc to bump my Str and Con to 20 and 18 for my fighter back up which started at lvl 5 (Party lvl). so I chose the Feat great weapon master to allow for more great sword damage and realized that if at lvl 20 I action surge with the four extra fighter attacks and so did my echoes that we would all attack 8 times and because of great weapon master you add proficiency bonus to heavy weapon attack damage. Ao I would get 40 extra damage and so would my echoes so 120 in total.

 I'm also at a loss what version of the game you're playing? You're referencing the 2014 rules with regards to gaining racial bonuses to ability scores, you're using a 2014.5 subclass, but you're taking the 2024 version of Great Weapon Master. If you wanted to go full 2014, you could deal +10 damage per attack, and, with a Haste spell, an Action Surge, an Echo, and twelve hits at a -5 penalty, you could do +120 damage, but you're just describing class features and feats working as intended.