Firstly, stretch marks may naturally occur because the skin has been stretched in a very short space of time.
Secondly, they fade! I had stretch marks on my boobs aged 12 (imagine how that felt!) but I actually cannot see them anymore. Eventually you’ll be able to use products to help reduce the effects of stretch marks.
To be honest, it’s a risk you take with the surgery, the skin is going to react when stretched suddenly.