**question 1**

the google translation is correct. Keep in mind that you can't translate word for word a language.
so "I have improved in math" would be "Je me suis amélioré en maths"

**question 2**

Google isn't correct, you're right. The correct translation is "Je n'ai pas que amélioré mes compétences".

Hope I helped! Use this website for translating (I'm french, but I use this for German): http://www.systranet.com/translate