[Always *]

You sound like you are being reasonable in your relationship! So you don't need to worry about that.
Now, going to be honest here, you probably should have honest with your mom from the get go. Now maybe you had a good reason not to be, but there is a possibility that your mom's anger is partially the outcome of her being hurt that you never confided in her (even if she led you to believe she didn't want you to be dating).
So it's to late to have done that. (just saying so for future reference). Just let her calm down and try to calmly talk to her later (don't tell her you love him though, use things like "I really care for him", declaring you're love will potentially upset her if she thinks you're to young to be in love), any ways, if she calms down it'll be easier to approach the topic, and you can explain why you never told her and stuff.
You're 17 and have a boyfriend, you're doing nothing wrong even by super conservative standards. Ok, so maybe the conservatives would be upset (no interaction between genders seems to be preferable to them when it can be avoided), but that's honestly ridiculous and extreme in this day and age. Any ways, like I said, you are doing nothing wrong. It's not like you are sleeping around (which is debateably risky - I worry about teenagers doing it because I worry about how responsible they'll be and if shit goes wrong, such as pregnancy a teenager is in a tougher position that someone in their 20's). So without reckless behaviour (sex with anyone who moves, drugs, jumping off cliffs, idk, choose your poison!) you're in the right here. But you need to take the time to hear why your mom is upset and respect it (ex. if you hear something you don't like, don't get pissed) and explain your perspective. If things start getting out of control, leave and revisit the conversation.
I hope you can work it out. It'll be ok.