I wasted six years of my life getting a PhD degree. What should I do, and how will I survive?
It looks to me like you did not do so badly as you think. Two publications and 3.7 GPA are not so bad. It might depend on the field, it might not be the best ever, but I have seen much worse. If your supervisor offered you a postdoc position after having you for 6 years as a PhD student, it means that they consider your work useful.

You might be suffering from impostor syndrome. Do read the question and the answers in that link and see if you identify.

If you are not sure now, you have plenty of time during your postdoc year to decide whether you want to continue in academia or get a job in industry. The pros and cons of both options have been discussed extensively, as a quick Google search for "industry vs academia" shows. I personally agree with this source.

And, in most cases, the answer to "I have wasted X years of my life because I did not do Y and Z" is "do not look at the past and do Y and Z now". Especially when, as  in your case, Y and Z can be done at any stage in your career life, such as learning languages, programming or driving.