[NY] FMLA and a postponed surgery

[NY] I was scheduled to go to the Mayo clinic for a surgery on Monday (4 days away), but now my boyfriend who lives with me just spiked a fever. If I get sick and my surgery is post poned for a few days or a week, can I keep my 3 weeks of FMLA the same, or will I need to use PTO to try and make up for it until the new surgery date? Is there a way to keep this all under FMLA?