I Can't Change My Template

I have been experimenting with the templates on this blog so much that the blogger platform has finally given up. This is what happened. I changed the template ( may be for 40th time) to Aspire by infocreek and I really liked it. But as is is my habit, i was playing around with html, experimenting with different positions for google adsense. I found a post regarding how to put adsense in the middle of the post. When I applied the code, as instructed, everything went berserk. I had two big ugly ads in one single post and 4 google adsense ads on the homepage. That was so frightening. I didn't know where the square block came from, as I had put the code for a rectangular ad. And I didn't know why the page was showing four ads. Google automatically shows not more than three ads on one page and if you have more than 4 posts on a single page, then the rest of the posts won't have any ads.
I had to delete Aspire and revert to this present theme which I had already saved for a rainy day like this. But now I can't put the code in the template, the blogger shows some kind of error message and asks me to contact support.
I used to put code in the html template, to wrap the ads around the posts, so if I had say, eight posts on homepage, then three will show the ad units and the rest of the posts got a blank space in that area. So I started putting only three posts on the homepage. But now I can't do any coding or changes in the template. :sigh: Lets hope everything settles down on its own, and I can get back to juggling htmls again.