I'm not sure if I have social anxiety disorder

The best way to figure out what is going on is to talk to a therapist about your struggles. Contemplating the reasons why meeting new people and social interactions cause you anxiety can give you and your therapist clues. For example: Are you afraid because you lack motivation to socialize? Are you afraid because you struggle to read facial expressions or read social cues? Are you afraid because you worry others will judge you, especially if you appear anxious? Are you afraid to say the wrong thing? Are you afraid others will hurt you? Are you afraid to be vulnerable or are you afraid of attention?

A lot of conditions can involve social difficulties, like social anxiety, autism, selective mutism, depression, trauma, or even some personality disorders. A therapist can help you understand the way your brain works, the why behind your behavior, and how to navigate social situations. :)

Social Anxiety is scary. You don’t feel safe in relationships and prefer to isolate yourself from the outside world. Is it something you can talk to your parents about? 

A school counselor could help you. The counselor could possibly order an evaluation to determine how to help.

Build your self confidence - Start slow with your family and identify a subject you are familiar with and add to a general conversation. It’s important to start finding things in common with others. You don’t need to carry the conversations, just add a phrase or two. Have an exit strategy if you get too uncomfortable. Keep notes of what worked and what didn’t work so you’ll be prepared for your next opportunity. Carpe Diem!

It certainly sounds like you have some anxiety. Before deciding whether it was social anxiety or a more general type of anxiety, I would wonder what it is that you think will result from you raising your hand or talking to someone you don't know. Here is some information on social anxiety: https://socialanxietyinstitute.org/what-is-social-anxiety

I would recommend talking to a local mental health professional. It sounds like your anxiety is affecting your daily life and there are lots of strategies that may help to lessen that.

Thanks for being brave to post here.

Congratulations on your courage to ask this question!

This shows you are willing to engage with other people, just not in all situations, especially the in person ones.

Start by "meeting" yourself.

Reflect as thoroughly as possible as to what you imagine will be the outcome of meeting others or of speaking up during a class.

Some people are afraid of being criticized or judged by other people, or do this to themselves inwardly.  

If you are judging or criticizing yourself to be less worthy of having opinions or views or of being who you are, than others, then the thought of actually placing yourself in this situation, would feel intolerable.

One way to move out from this position of feeling less than others, is to recognize that these feelings are inside of you.

Then it is possible to know at least on an intellectual level that it is not true that any one person is superior to another.

All the people whom you are afraid to meet, also have their own insecurities.

We are all equal in worth and in having blindspots about ourselves.

Also, it is possible that you are naturally shy and may be expecting more from yourself than is reasonable, in terms of a standard about meeting others.

You may have a few fears of being judged unfairly, you may also simply not enjoy being around people very much.

Be aware to not push yourself beyond your natural limits.  Overcoming fears of being judged is different than forcing yourself to do what is against your basic nature.