Do i have skin cancer??

omg..im so scared right now..
okay theres this bruise like thing on my arm and its about 3 inches i think?but the thing is..the bruise dosnt hurt at all and its been there for about 3 weeks.not just that theres a lump abotu 2 and 1/2 inches.i dont want to tell my parents just yet because i smoked weed on the 3d of march [this month] and i want to wait till its all out.and then tell them about the bruise and see a docter.

also when i pee its all clean its like im uranting water.
whats that mean?
im only 15...

it's a bruise!!! for heaven's sake, it isn't cancer, cancer doesn't present like that. A deep tissue bruise doesn't necessarily hurt, and it can last for months. Clear urine simply means you are drinking enough water. If you are so concerned, you need not wait to see a doctor, even if he draws blood, unless he orders a specific test for drugs, no one is going to know you smoked pot. Get it looked at and get reassured.

clear pee is a good sign, it just means you drink a lot of water, but you should show the doctor your skin, its probably not cancer if it looks like a bruise, skin cancer looks like a really ugly mole,

first off, skin cancer and the color of your urine are in no way related to one another. I have had skin cancer MANY times and know all the warning signs. The kidneys or renal system of the body controls waste products (urine) are removed from the body. Clear urine means you are properly hydrated so your drinking enough water. If your urine was dark yellow and had a strong odor you would be severely dehydrated and your kidneys would be seriously strained.

I am an expert on kidneys since I am living with a transplanted kidney. If your doctor took a blood test and the creatinine and bi carbonate of nitrogen (BUN) were high you would be in big trouble.

your arm just has a bruise on it not a cancerous lesion.

To add to all the good advisors above, yours is a classic example of "a little learning is a dangerous thing."
You may have heard from somewhere as cancer symptoms having the inability for healing of wounds and urinary and bowel disturbances and in your case, these are neither.
To avoid all this, enhance your knowledge by researching, the internet is rich enough, and develop a sound rapport with your parents, they will love you despite everything.