First, press the piece just the way you sewed it to set the seam, then press to one side. You can use a bit of steam, but be careful not to move the iron and distort the block.
Not 100 % sure by what you mean the ends of your block. Do you mean one block is shorter than the next? If that is the case then you need to verify that you are consistently using a 1/4" seam allowance. If you mean that a single block is shorter on one side than the other, watch carefully as the beginning and end of your seam maintains the seam allowance. I have found that I sometimes have to use tweezers to hold the end of the block together to guide that last little bit through, especially on weird shaped pieces.