At my last check up, I forgot to tell the doctor I have sarcoidosis. Is that ok?

Need to know. Your doctor needs to know, particularly if you have symptoms or are taking medications for it.
Must, must tell. This a very important disease that can affect the entire body, not just the lungs. If you have seen a specialist for this, please get these records to your doctor as this will likely be his largest health concern going forward. This was the disease comedian bernie mac fought throughout his career.
You just forgot. In the most severe cases---rare, sarcoid can cause sudden cardiac death; also rare--- need for an organ transplant! make sure that the specialist(s) you see for your sarcoid are true experts in this disease. Call your doctor and ask for a new appt to discuss your sarcoidosis symptoms and treatment. Some cases of sarcoid are quite mild or without sx. Rarely, are they severe.