New Thermal Paste Unstable?

Hello, my Toshiba laptop recently started overheating alot. It would often boost to 100C and then shut down. I finally replaced the old thermal paste with a new one. It was working great the first 2 days. It would idle at 30-40C and 40-50C when watching a movie.

Yesterday the idle temperate went higher. I did one test where I left it for 15 mins and it was jumping between 35-45C and then later I did another 15 mins idle test and it went as far as 50C. Is that normal or did I mess up the paste? I dont understand how it was great the few two days and is now acting up.

I should also mention that the fan is making more noise than the first 2 days. But the fan only covered the chipset and not the gpu.

I only put a thin layer of thermal paste over the gpu after cleaning it and then reattached the heatsink. Not sure if I need to open it again or if this is normal. Help pls.