your posts are from last year, but I have just found your site about a week ago.

I hope, you have some routine by now cutting your own hair; if not or if you have given up and want to try again, here is a way, of how you could do it:

Version A:
1) put your hair into a low pony-tail with a rubber-band [? (English is not my mother tongue...) a scrunchie would be to voluminous, so take a "scrunchie without a rim"], so that the hair is equally straightened.
2) slowly pull down the rubber-band along your back (so the hair stays equally straightened) until the rubber-band nearly reaches the point at which you want to cut your hair
3) then take the rubber-band carefully to the front and cut the hair
4) take the rubber-band off, let your hair hang lose along your back and check with a back-mirror if the rim is even; if not: cut the odd strands while looking into the mirror [okay, you have to get used to that, but it works with a bit of training]

or
Version B:
1) as in Version A
2) split the pony tail into two strands and take them to the front
3) cut the hair on both strands at the same level
4) as in Version A

or
Version C:

1) as in Version A and B
2) as in Version B
3) join the two strands with another rubber-band, pull the band nearly to the point you want to cut your hair and cut it
4) as in Version A and B

All these varieties require careful movement/pulling because otherwise the strand(s) may become different in length and then the result would be uneven…

I prefer Version B, because the hair is easiest to keep equal in that way. But try, which one you prefer.

Good luck,

Kerstin