Extra to what Mo said:
there's no problem with you feeling more room in your vagina. There are a couple of reasons why you likely felt more space inside you when you masturbated. First, the vagina changes size at different times. Ordinarily, the vaginal walls are closed together, and there's no space inside your vagina. When you're aroused, the vagina relaxes and expands, and creates a lot more room inside itself. If you were more aroused that time than you were when you've felt inside yourself before, your vagina would have had more room inside it.
Second, the position of the cervix changes slightly at different times throughout your menstrual cycle. (If you need information about the different parts of your body, see
Innies & Outies: The Vagina, Clitoris, Uterus and More.) Sometimes it's higher, sometimes it's lower. When it's higher, people often feel that there's more room inside the vagina.
(Also: if you don't get a reply quickly, please wait a day before re-posting your question. We're not staffed 24/7, and we will answer you as soon as we're able!)