Mercury square Midheaven - problems communicating (especially in public)?

[vannasan]

I would like to know if having Mercury square MC can show problems with public speaking or speaking in a group, or communicating in general.

I have my mercury in the first house, and it seems to be well-aspected except for the square to MC. In the first house I would think it would mean I would be an assertive speaker and would probably be good at communicating.
In contract, I never speak up in class or in public, even when I have questions or I'm confused because I know I will end up looking silly. If I do try to speak in public (maybe a presentation, or asking questions) as soon as I have the 'mic' my mind goes blank and the words out my mouth make no sense. Because of this I have social anxiety. This is especially weird because I have my MC in Libra, which should mean I would be a good speaker, or at least diplomatic (or is it charismatic?).

So anyone able to shed some light on this aspect, or know if it's easy to overcome. I will also post my chart, so someone can tell me if I'm missing another aspect.

*I've even joined a toastmasters group to help me get over it but...