I am feeling the same way. I love all the different elements and am happy with the result, but tying the tangles and the colours together so that they create a pleasing overall affect is not easy. There is a bit of trial and error involved. (Part of me still believes the true beauty of this Zentangle form is the black and white - where nothing catches the eye more than anything else. But I also believe that the colour does bring it alive.)
Since I have finished most of mine - and am actually running out of the supplies that I brought with me to finish the outstanding items, I decided to try doing a bit of a hit and miss border around the outside. And I think it is working.
What it is doing for me is bringing the very strong rainbow colours from the biggest motif to other areas of the matt that don't have those colours. So hopefully, when I am done, the border will encourage the eye to travel through the mat and not get stuck somewhere.
Certainly from an "art rule" point of view, it has the verticals, horizontals and diagonals - and I find that the beaded black and white line creates a nice pathway, but I really think this multi-colour edging will help pull all the colours to the outside.
Amazing exercise and I highly recommend both the Zentangle discipline and then the hooking of some motifs to anyone who wants to experiment with shape and colour. Such fun and so individual.
This will be the first of many for me, I think.