Yes, you should proofread it yourself. It doesn’t matter if you can spell or not, and I don’t care if you think grammar is your father’s mother. Go through and fix what you can. This is your book. Take ownership. You’ll feel better about it all in the end. Feel free to finally move the book from a plain text editor to a word processing program and use the spell-checker. Just remember that it doesn’t know everything. Stupid things have told me for years I was misspelling ‘Canfield’ but obviously, I’m not.
Now, get someone else to proofread it. Someone you know can spell anything.
Don’t let them make the changes. Have them note their recommendations. You get the right to accept or reject any change. It’s always possible they were wrong, just this once.
Once you’re sure all the words are spelled right and the sentences say what you mean, it’s time to edit.