thanks!
If the company offered you options at a different (lower) valuation, they would have to book the difference as a compensation expense to you. While it's technically possible, they are unlikely to want to do that.
Option backdating (getting equity at a previous valuation) is discussed helpfully here: https://en.wikipedia.org/wiki/Options_backdating
It's better for you to just ask for more equity.
However, realize that equity is usually worthless. If they already raised a lot of money, you're probably only going to get a tiny slice. If the equity is a factor in your decision to accept the job or not, you probably shouldn't.
Remember that the recent investors probably got a liquidation preference, which means they need to eventually sell for a LOT MORE than the price of their last round, or common shareholders may get nothing.