First of all, we connected our usb plug to arduino board (starter kit). After that, we completed Project 1 successfully (circuit with led and switch.) We tried unplug the usb cable, but it was very difficult, we had to pull very hard, but we couldn't unplug it. Finally, I managed to take it away with the help of my partner. I was pulling the usb and my partner was keeping the arduino board stable. The result wasn't very nice, we probably broke the usb cable. You can see what I mean in these images, the metallic coating part of the cable is still stuck on the board.
Nevertheless, we put the remaining cable back where it was, and the board seems to be working normally.
My question is if it safe to use it. Is there any chance of electrical damage or something like that?
P.S. In addition, we are planning to buy a new arduino starter kit. How can we avoid this problem with the new board?