My lowest note is a f2 in chest voice and a g6 in falsetto, my question is ... if my highest note is a g6 in falsetto how high can I get in a head voice? I want to know if using falsetto to get high is bad, thanks
It's the only way to get notes higher than one's normal range. Voice quality won't be the same, but there's no other way. Either use falsetto, or avoid notes higher than the normal range. Or change the key of the song. If it's only a few notes, the key change is by far the best and most used.
Chest voice and falsetto are two fundamental modes of vocal production. You can view them as two end positions of a swinging door, and the door gets blown at the more the louder and higher you sing. Falsetto leads to higher notes, chest voice to lower and more sonorous notes.
An unpractices singer does not have a lot of control over that door: it will be pressed closed in either direction and will flip over violently when going higher. Head voice is basically the chest voice position but taking a whole lot of load of the door, making for a much gentler transition if you go there. Mixed voice is having the door in an intermediate position and balancing it there. That's an elusive skill coming only with practice.
As a chest voice singer with little practice, any change to falsetto will be a jarring break in style, head voice will not come naturally and mixed voice is not available. This kind of hard break or flip is better avoided when performing: you want to appear in control of your voice rather than the other way round. Obviously dedicated practice can help you open that door.