Try to breath from the pit of your stomach. When we are anxious we often breath from high in our chest and we're tense further down. Try to breath slower and lower and focus on your asshole making sure the muscles in your pelvic region aren't tensed up.
Give your asshole time to accept the feeling of their dick inside you before they start actually fucking. A top's focus should be on your pleasure, not their own - if they want to get in there and pound away immediately, that's pretty boring on their part. Are you letting your partners know you are a little uncomfortable or anxious? If you let them know they might take it a bit slower to let you accomodate.
Try sitting on them, without riding, and just kiss and cuddle with you in control of when and how much you move, rock back and forth slowly if you like. Have fun. When your body feels more relaxed you can go to other positions for the actual fucking. You can even do the same thing in a missionary position, with them inside you and only fucking when you are ready.
Anxiety about making a mess is totally normal. Try not to eat anything too spicy or loose the day or two before (anal sex is never spontaneous I'm afraid). You know your own body and how it reacts to your diet, for me it's minced beef! I wouldn't even look at a spaghetti bolognese or cottage pie if I knew I was bottoming, lol. If you are not confident, then just say you don't want to fuck this time - there's a million other things to do besides penetration, they all end in an orgasm.Β :love: