Help with Offer negotiation

I am currently amid negotiations for a Software Engineer role. When i gave them a reasoning about my masters degree and my proven track record for my current role, they gave me a 5% increase on the offer. The offer is comparatively very low though. A person freshly out of masters got 15% better and so i am hoping to still negotiate. fyi, i have 2 yrs of exp.

when they first provided numbers, they were low and so i provided them with what i am expecting which was 20% more than what they were giving. since they came back with just 5% increment, how can i proceed with the negotiation ?

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