It is unlikely you damaged your SSD, but you did reduce its life a little bit. SSD's have a limited number of writes per sector. The SSD includes spares, and rotates physical sectors into logical locations (the operating system only sees the logical sectors) to ware level the number of writes to any given physical sector. But once a physical sector has been stopped holding data, it is taken out of the rotation and you have one less spare.
erasing free space or overwriting large chunks of the SSD will insure that a large percentage of the physical sectors wear just a little be more. If you do this a lot, then you will eventually wear out more and more sectors until you have no spares and your SSD starts to loose capacity and die.
Just doing the erase free space once, will be OK in the long run, but I strongly suggest against doing it any more.
If you are worried about previous file data in the free space, then use System Preferences -> Security -> FileVault whole disk encryption. Then when you delete a file, the free space is still encrypted data that is useless to anyone getting your SSD.