Hi Neptune,
Bad news. Just putting his penis back in would squeeze any semen (not precum but semen with sperm) into your vagina.
Timing wise, a few days after your period ended means you are increasing in fertility and nearing ovulation. Sperm can survive UP TO about 5 days.
Yes, there is a high chance of pregnancy. High being subjective. At best, when everything is "perfect" the odds of pregnancy are about 1 in 5.
Plan B is not very effective after about 3 days. While it may have some effect, by now if you were to get pregnant it's likely already too late. Conception takes about 3-5 days. Plan B will not stop a pregnancy after it has occurred.
You can take a home test as early as two weeks after having sex or your period is due. Testing early, false negatives are common. Use your first morning urine as well.
Good luck.