Hi Nuki26,
Welcome to the Apple Support Communities! I know it's important to make sure your Mac is working as expected. It sounds like your Mac is becoming warm while in use, and I'm happy to see if I can offer some helpful information.
In most cases, it's normal for your Mac to become warm while you're using it. This has some great detailed information that may explain what's happening: Keep your Mac notebook within acceptable operating temperatures. The tips below might help to ensure proper ventilation, and there are a few other good suggestions as well:
"Here are some tips to manage the operating temperature:
- Make sure that you’ve installed all Mac software updates and all current firmware updates.
- Use your Mac notebook where the ambient temperature is between 50° and 95° F (10° and 35° C). Don’t leave your Mac notebook in your car, because temperatures in parked cars can exceed this range. You should also use your Mac notebook where the relative humidity is between 0% and 95% (noncondensing).
- Use your Mac notebook on a stable work surface that allows for good ventilation. Don’t use your Mac notebook in your bed, on a pillow, or under covers.
- Don’t put anything over the keyboard.
- If your Mac notebook has ventilation openings, don't put anything into them.
- Use only Apple-authorized power adapters. Take steps to avoid overheating the power adapter."
Regarding any performance issues you're experiencing, there might be troubleshooting available depending on exactly what is happening. Feel free to reply back here with details. As far as returns go, you would want to get in touch with the point of sale to look into your options.
Take care.