Well, I have some good news
your backstay did not shrink. Worst case, your mast bend from improper storage over the winter.But I doubt that also and let's assume that did not happen.There are three things that could affect your backstay length. The first one, which you already checked is to ensure the headstay is not too tight. Do you only have one hole in the chainplate on the bow to accept the forestay? Maybe you could move it back? Also, did you connect the forestay and backstay to the same locations on the mast as last year?The second thing to check is the boot recepticle that accepts the mast. Is the mast seated straight and without interference? I have a little trouble here with my Mariner.Finally, completely disconnect (or completely loosen) the side shrouds, particularly the lower shrouds. You could be bending the mast foreward but I can not tell from your decription above.Was the receptical at the top of the mast bent?Keep looking, you'll figure out what it is.Best of Luck,Craig