I am due to feed my 8 month old corn snake tonight...?

It is a corn snake i got for christmas, in one of my previous questions i got alot of stick from some people about its conditions etc. The snake is in a plastic vivarium, holes in the top, heat mat on one side turned on 24/7 as someone advised me to do (i cant increase or decrease the heat it is plugged into the mains), and a hide in the middle of the tank. The water dish is on the opposite side of the heat mat, and when i feed her (the snake) i put her in a shoe box and close the lid. I was given pinkie mice from the store keeper he gave me about 8 so i can only imagine he has given me them the right side, they are frozen so i defrost them in hot water for about 20 mins before hand then put the snake in the shoe box and dangle the mouse by its tail and the snake has eaten it every time. Last time however i think it 'regurgitated'. I am scared incase it does it again this time and don't know if i should use a different method. I am 15 years old and in my defence, the store keeper told me absolutely nothing about anything regarding the snake except i shouldn't have a hide and a tank that is too big. He never told me about a thermometer or anything. I am using aspen substrate (wood chippings) and everything i have learned about snakes is off the internet and i feel the storekeeper should have given me alot more information. Therefore any mistakes u think i may be making i would like you to correct and hold the storekeeper at fault due to his lack of help!!!