Weight gain

I'm only 8 weeks pregnant and I have gained 2kg.. OMG right?? I hasn't been eating a lot infact.. just my normal 3 meals and a packet or milk in the middle of the night if I feel too hungry.. I would like to do some treadmill walking but am afraid of doing so as I'm still in my first trimester and I don't want to take any risk.... Yet I don't want to gain any unnecessary weight in my pregnancy. Any tips on weight management during first trimester?