A long time ago I wrote up a tutorial on iambic pentameter over on my other, family blog. I still periodically get comments on it. Like today Rachel asked for help with iambic pentameter, and pointed me to a sonnet she'd written: http://www.eliteskills.com/z/49778
I wrote back telling her about my new blog and how many this would be a better place to discuss it. Hi Rachel, I hope you stopped by!
If you're most concerned about the iambic pentameter, your last couplet is probably the closest if you flip a few words:
Forgive me, sir, for sins have I to tell.
Repent or not--condemned am I to hell.
There are times and places where you can get away with bending the natural pronunciation of a word (is it "washed", one syllable, or "wash-ED", two syllables?) but in general you need it to flow pretty naturally. I liken it to trying to play music without a beat. You can't really do it, you just end up with a string of notes and nothing holding them together. Your reader needs to find the flow immediately and not be left struggling for it.
A few years ago I wrote an Elizabethan sonnet for my daughter Elizabeth's first birthday, if you want to check it out:
I'm no poet, but your original question to me was about iambic pentameter, so hopefully that's an example you can work with that's not quite as hard to follow as some of Shakespeare's. You can clearly see places where I snipped a syllable here or there to fit the form (such as "e'er", one syllable, in place of "ever").