Not knowing exactly what recipe you used, it's hard to say where you went wrong.
My recipe is very simple and turns out great every time.
I don't measure, so I can't give you exact amounts of ingredients.
Ground beef - amount varies depending on fat content - extra lean, I use about a pound; chuck, I use closer to two pounds because so much is lost when fat cooks out
If I have ground venison, I mix it half and half with ground chuck.
Chopped onions
Minced garlic
1 or 2 eggs
Bread chunks (I freeze the heels from loaves of bread and use them for meatloaf)
Tony Chachere's
Worchestershire sauce
Loosely mix ingredients using your hands. DO NOT OVER-HANDLE! Too much handling will make the meatloaf tough.
Press into a loaf pan.
Bake at 375 until top is browned.
Note: I do NOT put ketchup or a tomato based sauce on my meatloaf. I pour off drippings as it cooks so that it isn't swimming in grease and use them to make a brown gravy.