Advise on Engagement

I got engaged about 4 months ago. I didn't get to see the girl much or talk to her more than a few times as it's typical in our culture. My parent really wanted me to get married to her but I had some reservations on her appearance. I did istikara at the time but I didn't get an answer. However, I said yes after my parents insisted, thinking she is from a good family and this will make my parents happy. After we got engage my reservation on her appearance got stronger. I live and work in a different city from my parents and the girl and only go home for a few days every month. I talk to her on the phone and she seems like a nice girl. But she's not the kind of person I imagined myself getting married too. I feel if I get married to her I'm won't be happy and will not be able to be a good husband that she deserves. On the other hand if I break the engagement I will hurt my parents and break that girls heart and she didn't do anything to deserve that. I'm very confused and it's effecting every part of my life. I have been doing istikara recently and I don't get any clear answer. Please advise me on the Islamic way to guide me. Also if anyone had been through similar situation please share.