Size when not erect varies considerably and is NOT an issue.
4-4.5" erect is within average for a 14 year old.
Average for an adult is 5 - 5 1/2".
Don't focus on your size. It's much more important WHAT you do with your penis.
Please use protection. A $1 condom is much cheaper than a pregnancy.
Your girlfriend will be VERY disappointed if you do not use a condom during sex and she becomes pregnant as a result.