I think it depends on the type of block some have points and you can very well be trimming off of point. With your blocks I believe if you trim evenly from the center of the block it should be no problem. The better option in my opinion would be to take those blocks apart and redo them to get better at you piecing skills if you are new to this the only way to get better is practice. Practice is what makes you more consistent because trimming down is not always an option so you can't always rely on that with every block IMHO