Did you get water based poly, rather than oil based poly? All oil based poly, irrespective of what it says on the tin, can be thinned with white spirit to make it easier to apply and cure faster.
Having just been through the same process, I found it more beneficial to mix up little batches as you go along. Doesn't matter so much then if you decide it's too thick or thin, just amend the next batch. After the initial couple of 50/50 coats, I mixed a slightly thicker batch for the next load of coats, with a thin batch at the end. Not that I'm an expert of course!