Can i use spaghetti noodles instead of fettuccine for alfredo pasta?

Of course! I interchange pasta all the time. Depends what I have on hand.

If the spaghetti noodles are all you have, yes of course.
But if you have other flat noodles (even lasagne, broken up) or short ones (bow ties, orecchiette, etc), they will hold more of the creamy Alfredo sauce.
For futures, see this helpful article:
https://www.foodnetwork.com/recipes/photos/pairing-pasta-with-sauce