First thing i would do is leave the animal alone for at least a week to 10 days or maybe even 2 weeks to let it acclimate to it's new surroundings. Also, i would not handle the snake during this time, especially if you offered it food. I do not handle my snakes for at least 2-3 days after a feeding, in order for them to properly digest their meals. If the snake is a male, and 3 years old, he can definitely handle hopper mice, my 21 month old Dodomas are easily taking hopper mice right now.
BTW, very nice Sand Boa

Chrissy
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1.0 Ball Python-Siegfried
1.0 BRB-Pedro
1.0 Blair's Phase GrayBanded Kingsnake-Elvis
0.1 Paradox Albino Sand Boa-Cleo
2.2 Dodoma's
0.1 pug mix