IF it is brand new send it back
A view of the underside with the mower standing vertical would be good
I have never seen one of this style of steering let alone worked on one
From the IPL I can not see anything obvious that would make the wheels turn too far yet still have them pointing strait ahead
I can see only 3 things that would cause this problem
1) wrong Selector plate gear part # 35 in the Sears diagram Part #440770
2) wrong
Lawn tractor steering plate # 19 in the Sears Diagram Part #194729
3)
Lawn tractor sector gear cap shown as #122 in the Sears diagram Part #444962
The first if too big would allow the drag links to move too much
The plate has 2 slots that the caps run in which looks like what acts as a steering stop
If they fall out of the slots then there is no steering stop
To me it looks very much like they are drawn in upside down and the flange would go to the top to prevent them falling out of the hole
I also noticed that no nuts & washers are shown so unless the selector plate is threaded I can not see what holds the drag links to the gear plate
Again this is just an IDEA from what I see in the diagram
However I note that all of the steering parts are flagged as "best sellers" so it looks like you are not alone .
A horriidly complicated work around for not using adjustable drag links in the first place
There is an old engineering addage which which goes something like this
"There is no design so simple that works so well that it can not be made more unreliable by making it more complicated "
A long winded way of expressing the KISS principle .