return URL doesn't work

I am using the SIM API in the authorize.net payment plugin, and when you click next in the shopping cart to enter your credit card info, the authorize.net payment page shows up like it should, and you enter all your info. But after you do and it approves/declines it, it just stays on that page and doesn't redirect to the url i posted. I need it to do that, or a way to open that up in a new tab when you click next. Any help?

Don't you have a link displayed on that page in order to go back to the shop and when you click on it it goes to your return URL ?

No, that is the authorize.net checkout page. No links on it. But I found a different way to handle that part, now I just need to see if I can make it pop up in a new tab instead.