change attaching back seat and today's practice

On the constuction page of python lowracer, the back seat has 4 holes to tie seat back folk.
I couldn't understand why 4 holes are needed. so I made just 2 holes.
However, through practice to ride python, unstable back seat makes harder to take balance.
So today's first thing is adding more 2 holes on back seat.

 I tied it like this. the rope is for shoes.

Back side. I tied it with one rope for shoes.

Today's practice. I set back seat angle to reclining. after this practice.
I noticed more speed to get balance. In the other word, I set too low gear.
I changed the rear gear to 3rd, front gear keeps lowest.
I got advice from someone, by pedaling, we can get balance. but if speed is enough higher, noneednes with pedaling, it must get balance in such case.
My muscle of arms has pain. they will become powerful.
Fine.