If the website lets you book it then you are all fine is typically my approach - unless you're likely to be changing it. I'd read it that you could only use it until 4/1, but I'd refer to my earlier point: website booking == its fine within the T&Cs. Sometimes a hotel would reuse a rate code for a different set of dates but forget to update the T&Cs - or extend an offer and again don't update the T&Cs.