Help! First time extension/Manemaxx user

I've never had extensions before, and I wanted a strand by strand method that wouldn't kill me, so I went with Manemaxx. I only bought the melting pot with the tembond, and purchased the hair separately. I bought 3.5 oz of virgin brazilian hair from *********, 16-18" weft. First, for some reason I thought that that size means that the longest hair extends to around 18", with many shorter hairs around 16". Instead, this hair was slightly over 16" at the longest, with a LOT of shorter hairs (all ranging from 2"-14"), so that my ponytail looks extremely thick, but I don't have enough of the longer hair to blend in with my own hair. For reference, my own hair is around 14-15". Because of all the short hairs, my install looks really ratty and I have no idea what to do with it. I am thinking about going to a stylist to trim it, but it looks like in order to make it look nice, we'd have to take off enough for it to be the same length it is naturally.

So my questions are:
1. Is that how hair sizes work?
2. What should I do now? (I did install all the hair and using as much of my own hair as I could without showing the bonds) Will it work better if I buy different hair?

Other less pressing issues
1. My hair is very stringy like unless I brushed it immediately before. This of course makes sense given the nature of strand by strand extension method, but I've never heard of this as a complaint from other people. Is there a trick to fix this?
2. Damn this hair gets hot... Something I didn't think about :-)




Last picture is just to show how thin it is on the bottom compared to middle.