Bro... one of my close friends started about 2 yrs ago and for the first few times he used to always 'freak out' as you did... the exact same things you've described.... the shaking the feeling when he sat down and he even saw some guy following him the first time... but he's much better now...

I would suggest you smoke with one of your friends who you feel comfortable with take in a lesser amount and don't try to fight the high just sit back and enjoy it. Just remember that ur using one of the safest drugs out there and nothing can happen... and as you start using it more often you'll relize the power of the drug and you'll be able to control it and then you can just chill and relax or get fucked out of your mind...

take it easy....

One Love