Im not feeling too great :(?

please excuse the capitalization and typos...im on my ipod. So today, i was supposed to go see my grandmom at the hospital before her surgery. Problem is, my mom and dad already knew they were going but did not tell me until last night. I knew that she was getting her surgery but i did not know that they were going to see her before her surgery. So, i had to stay up trying to get my homework done and cram with the little time i had (i would have had it done if i knew that i was going to see her, but i didnt). So i only got 3 hours of sleep and i still woke up, got my shower and got dressed but they kept rushing me so i told them to leave. I asked my dad last night what time we had to be there, he said 9.30 and this mmorning, they said 9.00. I am soo angry and sad because i really wanted to see my grandmom and its not my fault that my mom and dad did not tell me ahead of time. Now i feel really bad, they always do this to me and make it seem like my fault :( how can i calm myself down because i keep crying? I just feel so bad, i wanted to see her because she was just diagnosed with cancer and this surgery is major.