Media Encoder cuts off end when exporting?

Hi, I am on a time limit here. 

I created a video with a time duration of almost 3 hours long. I exported it through media encoder and let it do its thing on my computer overnight since it was a 9 hour process. When I woke up, I checked to make sure the video was good and I noticed the end was.. cut off? I repeated the process again to see if it'd include the end again. I even made sure at the export settings the whole video was included [with the blue slidey bar thingy under preview]. Went off with my day, came back and checked just to see that it cut off again. 

Then I tried just exporting the end clip only, which was successful with no cuts. Using adobe premiere pro, I tried to combine the main video and the end clip together. The end clip imports perfectly fine, but the main video just crashes the whole program every. time. It's really time consuming and really annoying- I don't have much time left. I looked up other posts in regards to this, but there was no solution in the threads. Has anyone else encountered this? If so, did you find a solution?

In the meanwhile, do y'all know any *free* video editors that allow me to combine my videos? It needs to accept at least 10GB of videos btw, I already pay for adobe products so I don't want to pay at a paywall for something I'll only use to just combine videos.