Since the serial number, IMEI, and warranty all check out, it’s very unlikely that your iPhone is fake, so that’s good news.
The slight size difference you’re noticing might come down to a few things:
Measurement variance: Sometimes tiny differences (like 0.1–0.3mm) can happen due to how you’re measuring or even the type of case/screen protector.
Model mix-up: Double-check the exact model name in Settings - General - About. For example, iPhone 15 vs. iPhone 15 Pro, or a regional version (some countries get slightly different builds or specs).
Manufacturing tolerance: Apple devices are produced within a very tight tolerance, but a small variation can still appear if you compare two devices side-by-side.
If the phone’s performance, camera, and features are all normal and Apple’s website confirms your warranty, then you’re good. But if the physical difference seems major or something feels off, you can always have it inspected for peace of mind at an Apple Authorised Service Provider or Apple Store — they can confirm right away if it’s a genuine Apple chassis or a possible assembly issue.
Hope This Helps:)