Both Mojave and annelabx told you 하지마 hajima correctly. 가 can be ga but it will be very tricky for you to tell it from 가(ga) and 카(ka). Because the sound 가 can be "glottal fricative". So you should get used to it. Also try 공 and 콩, 강 and 캉, 김 and 킴. If you need to hear the sound of ㄱ and ㅋ let me know, and I can record it for you.