Thanks for your query.
I read your query and I understand your concerns.
Following is my reply:
1) All the semen need not be inside after ejaculation.
2) Especially after standing up it will come out due to gravity.
3) Stay in bed after intercourse for 30 minutes and turn once on each side in between while lying.
4) Only one sperm is needed to fertilize. Hence dont worry about all semen staying in. Relax
I hope I answered your query. I will be available for any follow up query you have.
Dr. Mahesh Koregol
IVF & Infertility