Think the best solution is to cancel the holiday due to the virus.That way you will save yourself & the other two friends.Next time, be honest.
The holiday was almost twice as much as you told your friends! You were having to pay in instalments anyway. Didn't your friends suspect? Doesn't ring true, anyway.
I think you should get your two friends together and have a chat about this holiday, apologise and tell them the truth that you wanted to partly pay for their holidays as a treat, when you could afford it before the lockdown, but now things have changed and you can no longer keep up the payments. You can then decide between you whether you want to cancel the holiday or whether they can afford to pay a bit more or go somewhere cheaper. If they are good friends they should understand. I would be really upset to know my friend was struggling to pay for the extra cost of my holiday that I did not know about, and I would not want her to be in that position. However in future however good your intentions are, you should be up front, especially as this was a large sum of money you were hoping to pay towards your friends holidays. You may have been able to afford it in the beginning but you never know what is around the corner, as you have found out. Good luck.
I really feel for you, what started as a comfortable kind gesture has backfired. I lean towards being honest with them then you can decide what to do together.Otherwise, maybe borrow the money from family to cover the difference and live and learn to pay for things up front when you have the money or put the money aside. Good luck!
If you plan to get a place via 'clearing'
Lower your band & save £1,000s
Past-best-before health food etc