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
