Don't worry too much yet. I have a few 3 week olds that are still 65 grams since they are being stubborn about eating.
Try a mouse hopper. Bigger than a fuzzy but smaller than a just weaned mouse. As long as it is no bigger than barely wider than your snake is wide. Or a bit smaller.
I'd try this every couple nights until he decides to take it. Only start getting worried if he goes another 2 weeks without eating. Then you'll need to consider starting him by assist feeding him a thawed or pre killed fuzzy mouse.
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Snakes, Jeeps, Dragons, Nature, & Knives.. Makes my world go-round!