I've written both an undergraduate thesis (55 pgs) and recently finished a Masters thesis (94 pgs).
Is 50 pages doable? Definitely in the amount of time you have left. (I wrote the majority of my masters thesis in the span of two months.. the editing takes a while, however.) A little advice: start as early as possible. Have all the data now? Start organizing your data and writing, a little at a time.
(Just like everyone else has said..

) I prefer to work on one section at a time, myself.
I find the Introduction/Lit. Review the easiest to write, but only if I previously wrote a very in-depth proposal (does not sound like you had to, so.. it might be one of the harder, more time-consuming sections simply because of all the background information you have to look up, rehash in your own words, and organize in a logical manner.)
The Objectives section (if you include one) is rather self-explanatory.
Materials and Methods is far, far more detailed than for a typical paper. Thus, it takes up a gratuitous amount of space.. and time if you don't have typed-up versions of all your protocols. It's another relatively straightforward section.
The Results section is pretty straightforward too, just write the data up the same way you would for a paper. (Figures and Tables make it longer than you'd think..)
Discussion is a pain; be ready to write this part slowly and with much editing. (Otherwise, it's much like the discussion section of a paper.)
The abstract you'd write last, since it's just a brief summary of the whole thesis. (Beware of character/ word limitations. They should be in the thesis writing guidelines for your department.)
Make sure your reference program uses the format your department calls for..
Anyway, if you're determined to write a thesis it's more writing than you'd expect, but it's not the writing that takes the most time, per se.. it's the editing. (I spent a looong week changing the formatting around and trying to puzzle out their specifications!) Find several people, in particular professors, willing to help you by reading the thing and asking questions/suggesting corrections.. A good reader makes all the difference!
And remember: you not only have to produce a manuscript, but you likely have to present and defend that thesis too! (There's nothing quite like having a group of graduate students and professors throwing thesis-related questions your way after your 30-45 minute thesis presentation.. while a nice, briiiight spotlight shines on you.)
Ah, graduate school...
Good luck!