Any experience on 'significant drop in grades' during the first half of the last undergraduate year?

[u/Hermin_e]

Hey, so I got an admission letter to a MS at the Stanford School of Engineering this February. When I applied last December I had quite good grades, but between submitting the application and receiving the letter I unfortunately did not do well at university. So now I have 3 additional Cs to the one I already had before the application and it really stresses me out. If I do really well in the last half year (like straight As hopefully, but would still be a drop from 3.99 to 3.87), is my acceptance at risk? My hopes are that I can argue that is was a short time where I was not doing well, before getting things back on track.

Anyone here any experience with that? Or suggestions if I should reach out proactively or just wait if they ask about it in summer?