Friend being bitch

I'm 16 and I spent like £100 on theatre tickets for one of my best friends for her birthday - which was last month. The performance is today and I text her last night asking what time we were meeting and where and what she wanted to eat etc. AND SHE SAID 'Oh, I was going to go with Katie'. Another one of our friends. LIKE WTF I BROUGHT THEM FOR US TO GO TOGETHER. IDK WHAT TO DO I AM SO MAD.