The motor mount is plastic and not very strong. If you push on it hard enough, it will move. It basically holds the motor about an inch away from the firewall on four plastic legs. If one of these legs has buckled or broken, you will have problems. A slightly down and right angle to the motor is normal (about 2 degrees).
If it moves fairly easily, you will probably have problems in flight and you should investigate. Pull out the black plastic "engine" from the nose to get a better look inside. If it only moves a little you should be okay.
The plane will not handle a crash very well because the foam is fairly fragile, so I wouldn't take any chances on a loose motor or you might destroy the plane.
The plane is pretty easy to fly, so you shouldn't have any major problems. Just make sure th CG is right, all the control surfaces move (in the proper direction!!), and that you give it a firm throw from STRAIGHT out at full throttle. Do not throw it at a large upward angle or you might stall and crash.
By the way, here is a video from my Corsair maiden a few months ago: