Hi,
Your cactus looks like a
Opuntia humifusa. Do you grow it indoor or outdoor?
I grow it in my garden, it can go very low in temperatures. Mine survived -20°C, and it can go even lower.
For the marks, it can be nothing, but if you grow it inside it may be too hot/dry or not enough light.
Yann
(France, Clermont-Ferrand). Serre tenue hors-gel + pleine terre un peu abritée. -10°C tous les hivers.