1) Don't take two tests in a row. You've already got the data on your weaknesses from the first test. Why waste a second test before you've had time to work on your weaknesses?
2) Analyze those weaknesses and figure out a study plan for the next 2-3 weeks based on those weaknesses. Don't consider just content weaknesses - also consider process and timing!
3) You MUST answer the essays on your practice tests. Stamina is an issue on the test and the essays come first, so if you're not prepared to spend an hour writing before you can even get to the multiple choice, you're going to run out of energy during the real test. In general, practice tests should be taken under normal conditions - the whole thing, all at once, with 10 minute breaks between sections. If you can, you should also take the practice tests at the same time of day as you plan to take the real test.
4) Re: your careless mistakes. You can fix these. Make an error log (either in a notebook or in an electronic file). Note the problem source and number (so you can find it again). Write down all of the careless mistakes you made on this problem, think about (and record) WHY you made those mistakes, and figure out what habits you can institute to minimize the chances of making those same careless mistakes in the future. Made a mistake because you did something in your head? Write all your work down. Mixed up one formula with another? Make sure to write the formula down first, in its full "standard" form (eg, A = pi*r^2) before you start to plug numbers in. Answered the wrong question? (They asked for Billy's age and you gave Susie's age.) Write down B = ? and put a circle around it before you start doing the problem. At the end, glance back at the question and make sure you solved for the right thing. And so on.
Then, go start building those habits so you minimize the mistakes. Also, know that there are certain types of mistakes we each tend to make over and over, no matter how much we study. Know what those are for you so that the next time you're doing a problem that involves that thing, whatever it is, you can double-check to make sure you didn't make the mistake you frequently make. eg, if you always mix up the formulas for area and circumference of a circle, you'd stop for a second and look again to make sure you've got it right this time. You don't need to do that for every formula throughout the entire test - just the one(s) on which you tend to make the mistake.