Please complete your query by adding-

1. If not 2Kb amplicon, did you observe any non-specific band(s), if yes,

2. Please share your agarose gel picture to understand the issue

2Kb is a long amplicon. Have you given your polymerase enough time during elongation to complete synthesis?

Please review this info from IDT

https://www.idtdna.com/pages/support/faqs/what-are-the-criteria-for-choosing-pcr-amplicon-length-

and make sure your extension cycle time is appropriate for that size amplicon.

Also, what polymerase are you using? Have you checked what the maximum size of amplicon it can amplify is?