Introverts, when they are in an over-stimulating environment can get their energy drained very quickly. They might think that it was a good idea to go the party but they find the large number of people and maybe the loud music and in their mind the inane chatter is just too much and they will feel drained.
Extroverts will feel drained when they are alone. They will tell everyone that wants to listen that yes they like kicking back on the couch and doing nothing but after five minutes they want to get out, meet people and dance the night away. The couch is just too draining.
However, when you identify yourself as an ambivert you might not feel drained in either situation. You will feel at home lying down on the couch watching Netflix or you will feel equally at home at the bar or nightclub with a bunch of friends.
You know that you are an ambivert when you feel comfortable in any situation and it doesn't drain you too much although on the other hand both the couch and the bar may drain you equally. Whatever way that is how you know you are an ambivert.
Take being an ambivert as a good thing. You get the best of both worlds.
My own personal opinion is to get out there and have fun. You will instinctively know your limit and that is when you say your goodbyes. Don't let your extroverted friends try to convince you to stay. (and they will) No your limits and go home to fight another day.
Just remember, Ambiverts are cool.