okay i see some problems ...the one with red arrow together at top ..need to be merged ..that is one and the other straight arrow ...need verged also. the one with green need to be deleted ... then the straight red line ..mix it with line above in purple ..i would make a new line there with the split poly too keep good geometry, the orange line and verge with the above jaw ...if you dont understand dont be afraid to ask ... I am no expert just learning too but like i said working on same tutorial...

not at home to take a look at tutorial but have you merge the jaws and head ? not sure if that is at that part yet ?

of course this is just looking at the pic...maybe if the file is different i cant see it ...

but you are doing a very good job ...alot better than i did at first ...trust me I had all kinds of issues ...keep up the good work and any questions myself or someone else on here will be happy to help . heck i dont know it all but there are some very talented people here that know most of it all ... and are always glad to help ..