Would you be upset if...?

We have recently found out we are expecting our third child. We wanted to keep it to ourselves until we had seen the gynecologist to make sure all was ok. However..as many parents will know it's so hard not to!! So I told my mum and she swore I keep it secret. I also made it very clear to het that two members in particular I wanted to keep it from as we aren't on good terms although she is. With her "of course you can trust me!! I'm your mum!! If you can't tell me who can you tell??" Last night I found out she's called round and told most people..I'm fuming! I feel she betrayed our trust and not to mention rained on our parade, am I stupid in feeling like this?