Sometimes I like to measure the block to make sure it is square. It is kind of a quality control thing.
The less errors I make at this stage the better off I am when I go to sew blocks together. After you do this a few times you will be able to see when something is off. If you don't just say oh well and you take the time to fix it it will pay off as you sew things together.
When I start seeing blocks tilting to one side when I sew them together then I pick out the seam and look at the block to see if I missed trimming it to square.
That is my first problem solving tip. The first block of any structure needs to be straight so the whole structure will stand up to time.
I have this problem all the time if I get in a hurry so it is not a reflection on your skill it is a decision taken of whether to bother with this step or not. I highly recommend that you take time to trim if need be and to check each block.