How can I get my boyfriend's mom to like me?

My boyfriend have been dating for 10 months. during sometime around february his mom found a hickey i gave him on his neck. I know, a stupid thing to do. so ever since then she hasn't let him come over to my house. even if my mom or brother is there. my boyfriends birthday was about 2 months ago and i havent been able to get him something since he was in cali. well now he's back and i drew him something and i dont want to ruin it by hanging out outside. so he asked his mom if he could come over to get the present and she said he had to help her clean. it feels like she's making excuses. i know she probably does like me, but still, it makes me feel bad when i just want to see him. i also know she has a right after what happened with the hickey and all, but that was like 6 months ago.