First off - I wouldn't recommend Tren E for someone who only did Test previously. Tren is 5 times more powerful than Test. Additionally, Enanthate version of Tren makes it last in your system for a long period so in case something goes wrong and you stop the administration, it still lingers in your system for a week or 2. That's why is better to go Tren A. Should be used daily, but gets out of system faster. And you get to see how your body reacts faster too.
Tren should be used after you've used many other steroids and your body tolerate them well.
In case you still ignore my advice and go to Test + Tren; then at least, start slowly at about 200 mg Tren weekly. This means 1 ml weekly. Therefore, you only use 0.5 cc per injection (because you need 2 weekly injections).
In case you want more than only 200 mg Test weekly (because you can't separate them, obviously), you'll need another Test E vial.
So, 3 ml is too much for your needs, but you can still draw only 0.5 ml to use.
NOTE! throw away every syringe after use. do not reuse, otherwise you risk infections