Tidy/thin the top a bit by pulling or CAREFULLY trimming and shorten the length. It shouldn't look like it has been pulled, but the top should be a little tidier, and of course the tail needs to be immaculately clean- fortunately yours isn't completely white yet so you don't have to spend quite as long washing as you will need to in the future! If you look at some of the pictures in the Google search (Connemara show champions) link below it will give you an idea of how the tail should look:
i’d rake the sides very very carefully so it looks natural but not quite that natural haha, and feather the ends rather than cutting it straight across. when i bought diva she had a tail to rival a traditional, dreadlocks to the floor, but i’ve managed to make it look lovely and i’m certainly no expert! i like natives for that reason
Wash it to get it white then keep it in a tail bag give it a trim at the bottom but not straight across so it looks natural, I wouldn't touch the top as you really need that to grow down , on the day of the show you could wet it and tail bandage the top use some gel and hairspray to get it to look neater.
I have found the best way to thicken the base of a tail is to cut it a bit short, where it is starting to thin and let it all grow down at the same time. Probably not the thing to do at the beginning of the show season If it was my tail it would thin out the top lightly with a mane/tail rake. I am useless at pulling
ETA If the top is lighter , the bottom will look thicker
To feather the end, I either use a rake, and comb out the end on my knee, or the end of March plait the tail and cut the bottom off so it is not straight when the plait is out, time gives the ends a not cut look.
The top, do not use scissors, and just rake the sides lightly , not so it's bald or over short so it will lie between the cheeks, leave the top hairs, and bandage.