first, measure your finished HSTs (Half-Square Triangles).
are they all the same size?
are they all the correct size?
(hint: if they're all the same size you might be able to redifine "correct". ;-) )
which turns out too small? the strips of HST or the solid square?
if the square is too big, and the strips are all the same length, trim the square to size.
if the square is too small, the strips are the same, and you have enough fabric, cut new squares to match the strips.
if the square is too small, blah blah blah, and you don't have enough fabric to cut new squares, consider cutting the squares into quarters, sew them back together, and then add narrow strips to 2 sides of each square so you can trim them back to match the strips of HST.
or, you could take apart the strips and remake the strips using either a wider or narrower seam to get the length you need. as long as all your seams are the same width, the adjustment will work.