我只想说中文。wǒ zhí xiǎng shuō zhōng wén But it sounds a little bit blunt. You can be more tactful by saying 我可以只说中文吗？我想多练习练习 wǒ kě yǐ zhǐ shuō zhōng wén ma, wǒ xiǎng duō liàn xí liàn xí. (Can I only speak Chinese? I'd like to practice more.) I can only Chinese with you, if you'd love to.

not rocket science

I'm sorry to tell you that "normal" is the most widely-used English word for "师范". We don't have another word. Besides, we have "工业大学" (university of technology), “财经大学”(university of finance and economics)“政法大学”(university of political science and laws)“医科大学”(medical university)“农业大学”(agricultural university)"综合性大学"(comprehensive university, but usually this type of universities are named after the place they are located)"戏剧学院" (academy of drama),“军校”(military academy)“航空航天大学”(aerospace university)“海洋大学”(ocean university)“海事大学”(maritime university)"外国语大学"(university of foreign languages),etc.

It takes more than just a "Sorry", you need to do more to make it up.