kind of ... well, actually ... while you only need one nomination, having more than one can help some candidates. The reason is that you are placed into multiple "pools". If you have a Senator nom but you end up being the 2nd best candidate on that list, you will not get an appointment. If you have also got a Rep nom and happen to be the best candidate on that list of 10, then you get the appointment. Since both slates presumably are have different candidates, you may rank differently on each slate and could get an appointment from one whereas you may not from the other. Similar scenario if you have a Presidential nom. If you have a MOC and a Pres the SA may decide to pull you as one of the 100 pres slots and give the #2 guy on your MOC list an appointment too.
It is a very complicated thing - and the truth of the matter is that you only need one nomination and the SA will only charge you to one nominating source. However, having more than one nomination gives the SA options for how they may be able to shuffle things to end up with you. This is another reason so many people frequently advise candidates to apply to as many nominating sources for which they qualify.
I am hoping it will not affect anything, because both of my senators said I was qualified and would nominate me, but because I was already receiving a nomination from one, the other decided to give his to another person so more people could have a chance
so, it will not matter that I received 1 instead of 2?
It sounds like your Senators are coordinating their efforts, very common. Typically that means they also try to coordinate with the noms from the Reps too .... The fact remains that you only need one nomination to gain admission. If your MOCs do not allow for more than one for you it is fair to assume they don't do it for others either ... in which case you're doing the best you (and your immediate competition within your district and state) can do. While it helps admissions, if they want you then you have a nom which is all they need to appoint you. Present the best "you" possible to the SA and if your best is their choice within your nominating pool (slate of 10) then you get an appointment. If you are not the top of your slate, you go to the National pool and see where the chips fall. They will pull candidates from the National Pool until they fill the class. The same scenario holds true even if you had 2 nominations - if you were not the 1st selection on the slate from either senator, you'd still end up in the National Pool.
Bottom line - don't stress about that which you cannot change. Be sure you have presented the best you've got and wait.