There are definitely rashes that can develop from being out in the sun for too long. One of these is called heat rash or 'prickly heat'. This often develops when sweat glands get plugged up with dead skin and other debris, causing red bumps to form on the skin. This can usually just be treated with good skin hygiene and waiting things out.
The other possibility would be that you have a sun burn, often showing up as a red, warm, or painful or uncomfortable area of skin where you were exposed to sun. Simple sunburns can be treated by keeping the skin clean and dry and well moisturized, as well as taking an anti inflammatory medication such as ibuprofen. However if there is any blistering or severe pain you should go ahead and talk to your doctor
In the future, you should be careful to protect your skin. 6 hours of sun exposure is a lot of sun exposure. Over exposure to the sun puts you at risk of premature skin aging as well as skin cancer. Make sure to wear sun screen at all times when out in the sun.
Please check in with your primary care doctor
for more information.