The rule of thumb is if you run your finger nail over it and it catches on the scratch then you will need to get the panel resprayed unfortunately
Although one thing that can be done is if you get touch up paint (obviously same colour as the car

) and fill in the scratch.
Building up the layers of paint till its roughly the same level as the surrounding paint.
Leave this to dry properly, then what you would use is a technique called wetsanding, where you use increasingly fine sand paper to sand it the touch up paint back to flat.
The sanding marks are then sanded out using a machine polisher
This is not a 100% correction method, but in many cases can vastly improve the mark.
But on the downside its not a job for either the faint-hearted or the less experienced.
My advice would be to contact a Professional Car Detailer in your area, and ask them to come take a look at it. You may be looking at the good side of £100... but in my opinion, well worth the money and much better than paying for a full panel respray
Hope that helps