Congrats on writing your first novel. I'm right there with you. I wrote the first draft to my first novel in 3 1/2 months this summer. I'm currently writing the sequel and will begin editing my work when I finish the first draft to the sequel. Honestly, I don't think they're good enough to be published, as I'm still learning, but I've learned a lot while writing them. I already have an idea for the third novel I'm going to write, and can't wait to get started on it. Hopefully, one day I'll become a published author.
AskMaryn offers good advice. You WILL be rejected if your novel has too many grammar errors; it's a sign of poor writing. It WILL be rejected if your characters and plots are not well developed. It WILL be rejected if there are plot holes. It WILL be rejected if your storyline is fatally flawed. Yes, a publisher will help it's author improve it's book to make it more markedly viable, BUT, you must have something for them to work with. If you have to rewrite the whole thing then they'll reject you and publish someone who has shown the ability to write a nearly perfect and marketable novel. You have to prove that you have what it takes to be published. The editor isn't going to hold your hand and guide you with baby steps on how to write a good novel - that's your job to learn on your own if you want to become commercially published.
NEVER EVER submit work that's poorly written, has many grammar mistakes and flawed plotlines because you will have just wasted your chance at getting your work published. What I mean by this is that once send a query letter to an agent or publisher about your book and they reject it, then you can Never query them again regarding this same project, so that will be a missed opportunity.
Publishers know that everyone who submits their work won't always have something that can be immediately published, but you have to give them something to work with. Publishers, and agents, will always suggest changes to your manuscript, but they're not going to take on work that needs to be completely rewritten, but work that's nearly perfect, but not quite there. THe changes could be anything from rewriting the ending to deleting a subplot.
It's good that you're not taking your mom's word and running with it. And, yes, you will look unprofessional if you send something that's badly written. BUt, I've read from publishing editors (they have weblogs) that 90?f the people who's manuscripts they read have horrible grammar and that alone will get it rejected. At least show that you know how to write a novel, and just putting words on a piece of paper doesn't prove anything.
You also have to be very careful with the very first novel you've written. Usually, people's first novels aren't publishable. Many people have to write several unpublishable crap before they start writing gems that stand a chance of being published. Even Stephen King wrote 4 unpublishable novels before he finally got his first one, Carrie, published. The more you write, research, study, and read then the better you'll become at writing. Edit it, and edit it some more. Look for continuity, edit for grammar, and make sure your plots and characters are well developed before you send it off. Then edit it some more. Let family and friends read it and provide feedback, and also let other writers critique your work and provide feedback. Writers are more reliable, especially authors or those who are aspiring authors because they've most likely studied the elements of novel writing for their own projects and know what to look for that your average reader (family/friends) wouldn't think about.
Yes, publishers have editors who will edit your work, but they are only used for work that has potential. Inherently flawed plots, under-developed characters and plots, and bad grammar does not show potential. It shows that the novel is as badly written like 99?f the other manuscripts they receive, and you will be rejected. Good luck.
You can get feedback from other writers at
http://www.absolutewrite.com/forums - you have to register to see the Share Your Work forum.
Also, many literary agents and publishers have weblogs that you can follow.
http://nathanbransford.blogspot.com and
http://pubrants.blogspot.com are two blogs by literary agents. They give GOOD advice about how to get published and what they look for in manuscripts. Read and learn how the industry works. They also link to other good resources.