You might want to move right on to experimenting with a partner, and this is also another way to learn about your ass. Say to them "I'd sure like to enjoy anal pleasures, but I'm not used to it and a little afraid," Then your partner they can turn you on, after douching if necessary, and that they can place their fingers at your anus during sex. They can also suck and tongue your anus if they like, or insert their finger(s). These are called analingus and postillioning, and can be soothing, warm, and exiting. A nice thing is for your partner to masturbate you as their finger is inserted in your rectum.

If neither of you can get this far, because your anus just won't relax, it means you're anxious somewhere, or you simply don't know how to relax it yet. This is not always the easiest thing to learn, and there's no reason to feel bad about it, since the anus is very likely to just follow old habits of not opening up. It takes time. Take risks only when you really feel safe, and don't allow yourself to be forced open. It helps to talk about this, and how you're feeling.

One especially nice act that can relax your rear is for your partner, during sex, to simply trace soft rings around the opening, pressing with one or two lubricated fingertips, going around and around. This usually has a calming, wholesome effect.