It is highly unlikely for a full-fledged peer review to be completed within two days. Even journals that have a short article processing time take at least a week to 10 days to complete the peer review process.
It is possible that for this journal, “under review’ refers to internal review or initial screening by the editor. Another possibility is that this is a rapid publication journal that publishes articles after a quick internal review and has a system of post-publication peer review. There is also the possibility that the status has changed by mistake, due to some error in the system.
Lastly, please ensure that the journal you have submitted your paper to is not predatory. I hope you have checked the journal website carefully and consulted your colleagues about the reputation of the journal before submission. If you have not, please do so immediately. If your paper is accepted meanwhile, write to the journal asking them to withhold publication. Be completely sure of the reputation of the journal before you give them the permission to publish.