Kissing another girl on the weekend does not necessarily mean you are a lesbian. What it does mean is that you are open to exploring your sexuality and that kissing a girl was part of that exploration. Sexuality is fluid, meaning it can change over time. At this stage in your life you may feel more attracted to females, but as time goes on your attraction may be more towards males. Or, you may be equally attracted to both genders.
I encourage you to let go of ‘labels’ e.g. lesbian, gay, bisexual etc and instead accept yourself as somebody who is exploring your sexuality. On the other hand, if you feel like you identify as a lesbian then that’s awesome that you feel clear on that. The best way to move forward and seek extra support would be to connect with your local youth centre, school nurse or talk to a trusted adult who you can chat to and feel supported by. Find more information on same sex attraction here.