Want a fair offer for injury claim

Hit by a car that ran a stop light. Car totaled and his insurance paid for it. Was an older, great car but what they gave was low. Said couldn’t negotiate it. I went to the dr that day with neck pain and stated possibly strain and gave a perscription. Missed 1.5 days of work. Insurance offered $600 plus up to $1500 medical coverages for 2 months. Shortly after accident staring having occasional headaches and a couple episodes of tinglinging the fingers and arm strength in left arm. This recedes after a day and may return a few days later. Anyway, I’m unsure what to do. My concern is if I accept and 6 months down the road gets worse, I’m in trouble. So, should I take this offer? I would prefer to counter the offer but not sure what to ask for. Or, should i not accept any low offer and just keep claim open until it expires, giving me protection if something dos come up. For $600, I would gladly give up for them to be liable for longer in the future.