Sawsang that lanyard looks OK to me, BUT keep in mind the Regulations for your area. There is probably something that says "meets or exceeds rating 1234".
The "snap" you are going to use is likely the most expensive part of the DIY lanyard. I believe they have to have two separate actions to open, if you have one and it is properly rated, I know what I would do. I think that even the termination at the snap is dictated by the regulations in YOUR country.
I would just feel awful advising you as to what to do, and have you disqualified from the course for non-compliance of equipment. So here is what I suggest, go buy an approved, manufactured lanyard. You will have the benefit of its use for years to come. Everyone needs at least two anyway.
Where I live, it is manditory that there is another complete climbing kit, including spurs, on-site at all times, in the event that someone needs to be rescued.
It is probably a real good idea that someone is there that knows how to use it.
So now you know that this occupation is equipment heavy, and expensive. Ya STILL want to be a tree worker?