Hi,
I'm only coming to the end of my first year but, from what I've gathered, the final year may not be the worst for Humanities students PROVIDED they've been focused and writing consistently throughout. In my (humanities) dept at least, some people seem to put off drafting chapters for as long as possible. Obviously this is will delay them further on.
I think that with Social Sciences / Hard Sciences your time frame is very much determined by your data collection / experiments and this can delay the writing up process until the final year(s), leading to a very tight race to the finish.
So, I don't think you should be worried that your task seems manageable. Instead you can be proud that you worked hard from the beginning.
(up):-)