A condom was used, he ejaculated into the condom; about 15-20 minutes later he put himself back in (he was dry). should i worry about getting a plan b?

Use Plan B : Anyone having intercourse without birth control or condoms may get pregnant. If intercourse was within 72 hours you consider taking plan b. Ella (ulipristal acetate) is another brand that can be used up to 5 days after unprotected intercourse. Plan b is a high dose of birth control to disrupt the hormonal patterns to delay or prevent ovulation. Abnormal bleeding after is common. Check preg test in 10 days.

Yes you should: While pregnancy is not likely, the real question should be "how much risk do you accept in becoming pregnant, and are you ready to be pregnant?" you are a teen-ager. If you are not ready, you should modify your activities and use proper birth control.

Yes: Regardless of ejaculation and being dry afterwards, if there is no protection there is always a risk of leftover ejaculate and semen that may still be transmitted to you placing you at risk for conception. This is a lower risk but a risk nonetheless. On top of that, there is always risk of stds with no protection.