Help: can't get day off for college interview

Hello,
Recently i found out i have a college interview on the day i am working. I cannot change the interview as it is unlikely to be rearranged because so many people apply. i therefore arranged a shift swap with another colleague however they said they could only work 2-8. I work 2-10. I didn't really think my boss would see the problem as it is only two hours gettting missed. But the thing is he refused it because someone needs to be on the last two hours. Which is honestly bs as today the guy who was on to 10 got sent home at 8 so no one was in then. I know i sound like a whiny person here but education should always come first and the company itself promotes it's flexible working scheme. I would use holiday hours but i have none left because obviously it's the end of march and that's when the year of holidays end.