Dealing with a sharp high G
If you have a sharp high G you can expect to have to put some tape on the hole but if the tape gets close to or covers half of the hole squealing will likely occur.
If you are fitting a new reed the problem may simply be that the reed is just too dry and needs to take on some moisture in order to bring the pitch down. Chanter reeds do need a certain amount of moisture to play properly. A moisture control system is a must but you don't want something that will take all the moisture away from the chanter reed. A good balance must be struck. If, after playing for a while, the note doesn't fall into line then some adjustments will need to be made to the reed.
First, check the mouth size. If it is too small, use a mandrel or reed poker to open it a bit. A good indication that the mouth is too small is a thin sound and an overall pitch that is too high. Opening the mouth will broaden the sound of the reed and bring the pitch down, especially on the top hand and even more so on the high G.
If the mouth is a good size then the blades will need to be thinned at the tips. This must be done with caution as you don't want to sand through the tips, just thin them. Sand the top 1/8th in. with some fine sandpaper. I use 320 grit. If this doesn't quite get the errant note to where you want then scrape the reed with a blade just below the center line of the reed in an oval shape. A combination of opening the mouth and careful sanding will bring the high G into line.