Can you get Carvana to raise their offer when selling?

No. Carvana's sell offer is algorithmically generated and cannot be negotiated higher. You can resubmit your vehicle information if you believe you made errors in your initial condition assessment, which might change the number. But the most reliable way to get a higher offer is to get competing bids from other buyers. If Carvana's number is the best, take it. If not, you have better options in hand.