Recently had PRP where they spread it on the scalp and used a dermaroller over it, is this the correct method?

This is not ideal.  The dermaroller will not be able to get it into the correct layer for optimal results.  The PRP should be injected into the scalp.  In addition, microneedling can be used on top of that.  There is a big difference between microneedling and a dermaroller (microneedling can go a lot deeper).

I believe that injecting the PRP down around the hair follicles is more effective than using a dermaroller. The scalp skin is very thick and the dermaroller will only allow penetration a small distance into the skin and not down around the hair follicles. Every hair restoration surgeon varies though in their techniques. I recommend discussing your concerns with your hair restoration surgeon. Good luck!

The effective treatment is to take the Platelet Rich Plasma and injected into the scalp around the hair follicles. Microneedling with PRP is a technique than can be added on top of this procedure but by itself will not reach the desirable level.