Yes, definitely, if you are not satisfied with the repairs, take it back.
Is it the replacement panel that doesn't fit, or the bonnet lid? If it is the lid, it might just be a simple adjustment.
There are all kinds of things that happen to cars when they get smacked, and other bits get bent out of shape that you can't see. The impact doesn't have to be that hard. So it is possible that they haven't fixed everything that they ought to have done.
I was shunted in the back at the traffic lights once and there wasn't a mark on the outside of the car, but the floor pan in the boot had rippled up and there was quite a bit of damage to the underneath of the car that you could only see when the car was on a ramp.
I would be inclined to take it back and see what the garage says first. If you have no joy, contact the insurers.
In the meantime, do you have a tame mechanic who could put it on a ramp and have a look at the the ca from underneath?