All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
There is essentially no harm in the semen touching the matting because sperm is ritually pure according to the scholarly opinion adopted by Islamweb. This is also the opinion of the majority of the scholars as underlined in Fatwa 85710. Hence, there is no harm if the semen touches the matting or any other item.
Allaah Knows best.