Thanks Superman. Keep sanding, it will be worth it in the end!!
Right then, next update. I decided to get the arrows and the dent done then prime the dome so any little dents/scratches etc will become a bit more obvious(and I'm also very impatient!!!!

) I used Alan's templates to do the arrows. They still need a bit more work but I'm happy with the position of them.
I used Boba Swede's dent template to get the dent shape and traced a bit more of the surrounding detail to orientate myself a bit better. I know some of a us newbies struggle with the dent position, but I figured that getting as much detail to refer to is the way forward to getting it right. Everyone's dome is going to be slightly different when doing a scratchbuild so there is no point in using exact measurements to the milimetre. What I did to estimate the position of my dent was to take line across the top of the left arrow(facing out), the black line on the attached pic, and draw two reference points from this to orientate the position of the dent. Take a look at the attached pic to see how I did it. It's easier to demonstrate it than explain it in words. BTW, A line taken directly upwards from the left hand vertical edge of the visor bisects the point between two easily discernible scuffs on the Boba Swede template. This immediately makes life easier. The other point to determine is up to you. Just record the angles on the ref picture and transfer them to your helmet.
Looking at my dome, I'm quite happy with it but, I think the dent may be a bit small:confused, although it is the 2.5cmx2.5cm as quoted elsewhere! Hopefully, when painted it will look ok.
Well, too late now, I will crack on and get the next few bits done. If any of you guys see anything glaringly obvious then please tell me before I get too far into this project