PLEASE HELP IN PHYSICS!! (ENERGY)?

This questions have part A and B. I got part A right but i cannot seem to figure out part B.

The question is
NOTE EXPRESS ANSWER TO TWO SIGNIFICANT FIGURES.

The mass of a carbon atom is 2.0 x 10^-26 kg.
A) What is the kinetic energy of a carbon atom moving with a speed of 410 m/s?

i just used the kintetic energy equaiton KE=1/2mv^2 so KE=.5*(2.0 x 10^-26 kg)*(410^2)=1.7*10^-21 J

B) Two carbon atoms are joined by a spring-like carbon-carbon bond. The potential energy stored in the bond has the value you calculated in part A if the bond is stretched 0.050 nm. What is the bond’s spring constant?

so for this question i used F=-ky
F is already known from previous question and y is given in nanometers.
so i did
1.7*10^-21 / 5*10^-11 = 3.362*10^-11 == 3.4*10^-11 N/m

i tried this answer but got it wrong so i tried it with a negative sign and still got it wrong.
So i am not sure what i did wrong here or if my units are wrong? isnt the spring constant in N/m ??

Please help 🙁

Thank you

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