It may get quite frustrating, but can also be a lot of fun, to try to guess one's own ascendant.
I had to go through different rising signs trying to narrow my choices; but in my case I was confused between just 2 signs.
It does help to go online, or otherwise, to read the traits of each ascendant, and see if one fits more than another; afterall they are only 12 . It also helps to print them out and share this information with your closest friends as they will probably give you some new ideas and insights into the you that you may not be aware of .
Rising signs are essential in the sense that you will know which planets, including transitory ones, fall into which houses, and most astrologists claim that this bit of information is the essence of really understanding your own birth chart and/or transits.
However if all fails , an alternative is to study your birth chart in relation to your Sun Sign. I have found tremendous insight at times, learning through this one alone, and considering it as an ascendant,i.e. your 1st house, in your case this will be Sagittarius ( I guess ).
I was once told,, by a noted astrologer, that the most important 3 signs and aspects thereafter in the birth chart are the Sun, Ascendant, and Moon signs - Not necessarily in this order though.