Do I fight for my wage increase or just accept that I put myself in this position?

I am an apprentice in a union that requires us to take training at the hall before we can receive pay increases when we change terms (2nd year to 3rd year, etc). I have had no issues obtaining a seat to get the previous 3 levels/weekends of training. The course I am required to take has been offered to me three times in the last couple years. A letter is sent out each time to all the apprentices needing the course and we have to call in to book our spot - first come first served. I was unsuccessful in calling in fast enough in order to secure a spot for all 3 offer letters thus far - the 3rd training opportunity scheduled to happen in a week's time. I was also scheduled to switch terms and receive a decent raise around the same time. I am told I can only wait and try to secure a spot in the next class - 6 months away. Several thousands of dollars in wages lost over that time period. I have taken responsibility for not receiving the letters quick enough (IMO should be sent by e-mail or phone - but this will likely never happen).

I had a meeting with the union committee and they did not seem to have much faith in the contractors having any sympathy for my situation - especially considering one of the letters took me 3 weeks to respond to from the mailing date (Partner had placed the mail down in a very hidden spot - she felt bad (I did not get angry with her)). The other two letters took me about a week/week and a half to respond. I wrote a letter to the contractors committee, asking if I could take the course outside of the hall on my own dime, or receive an extension or exception to the rule requiring this training before I could receive my increase. They denied all requests. The training consists of two days - the first day is composed of a course taught by an instructor, which is available to the public (This I could get on my own tomorrow) - but day two is taught by a board member / contractor, which is something he created specially for the apprenticeship (Not something I can get on my own).

The situation has caused a lot of anxiety and stress over the last few weeks. I feel like the situation is unfair in that those who were unable to book a spot fast enough on the first offer should be given priority or at least a heads up for when the next training offer comes around (it's twice a year, no known dates until we get the letter). But I'm told there is no 'hand holding' for apprentices, it's the same shit sandwich for all of us - therefore it's fair. The course used to accept 25% more seats in the recent past. There is also one other apprentice in my exact situation right now. We are told we can show up on the day of the course and if someone no-shows, one of us can take their spot (not me - other guy asked first so I guess he gets dibs). Absolutely no switching allowed, because supposedly every apprentice that successfully booked a spot would be in our shoes missing out on a wage increase if they gave up their seat...

I don't know what to do at this point. I feel I've exhausted all my options. Do I just accept my loss and check my mail daily in hopes that I can get book a seat for the next class 6mo from now?