No, there is no particular risk of semen (cement) left in your rectum. Most of it will spill out of its own accord with your next bowel movement, if not before. The trick in your situation is to be very sure both partners are truly monogamous. This means that neither you nor your partner are enjoying a quickie here or there on the side. It's a good idea to keep communication open so you can both continue to be assured of your sexual health. If you or your partner have other partners, you should continue to get checked for HIV and STDs every 3 months, and talk to your provider about whether PrEP is right for you