I am an undergraduate student applying for a study abroad program that requires I submit two letters of recommendation. I just received the notice that the deadline for submission is in two weeks and in my frenzy to get the letters, I contacted a lot of TA's and professors. Since then, I've already had two TA's agree to write letters on my behalf, but an additional professor and TA also agreed to write letters for me. Is it rude for me to let them know that I've already found someone else? But I'm also worried that it's simply such a waste of time to let them continue with writing the letter. Any tips on how I can politely let them now it's not necessary anymore without jeopardizing my chances of potentially getting them to write letters for me in the future?
It's ruder to waste their time. Just send a simple email saying "Thank you for agreeing to write a letter for me, however I realised I accidentally asked too many people to write letters for me for this position, so you don't need to continue writing one for me. I would still like to ask you to write a letter for me in the future, if I decide to apply to other opportunities. Is that ok with you?".
Either they will agree, in which case great, or they'll say no, and eventually you will have to find someone else. My advice would be to ask your letter writers a long way in advance of the deadline, to avoid you having to rush around asking multiple people at the last minute. You will likely get a stronger letter that way too.